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Extended version of Rambda - a lightweight, faster alternative to Ramda

Package Exports

  • rambdax

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (rambdax) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

Rambdax

Extended version of Rambda(utility library) - Documentation

Rambda is faster and smaller alternative to the popular functional programming library Ramda. - Documentation

CircleCI codecov dependencies Status Commit activity All contributors Library size

Differences between Rambda and Ramdax

Rambdax passthrough all Rambda methods and introduce some new functions.

The idea of Rambdax is to extend Rambda without worring for Ramda compatibility.

Example use

import { compose, map, filter } from 'rambdax'

const result = compose(
  map(x => x * 2),
  filter(x => x > 2)
)([1, 2, 3, 4])
// => [6, 8]

You can test this example in Rambda's REPL

Rambda's advantages

Currently Rambda is more tree-shakable than Ramda - proven in the following repo.

The repo holds two Angular9 applications: one with small example code of Ramda and the other - same code but with Rambda as import library.

Currently the Ramda bundle size is 2.03 MB less than its Ramda counterpart.

actually tree-shaking is the initial reason for creation of Rambda

  • Speed

Rambda is generally more performant than Ramda as the benchmarks can prove that.

  • dot notation for R.path and R.paths

Standard usage of R.path is R.path(['a', 'b'], {a: {b: 1} }).

In Rambda you have the choice to use dot notation(which is arguably more readable):

R.path('a.b', {a: {b: 1} })
  • comma notation for R.pick and R.omit

Similar to dot notation, but the separator is comma(,) instead of dot(.).

R.pick('a,b', {a: 1 , b: 2, c: 3} })

// No space allowed between properties
  • Typescript included

Typescript definitions are included in the library, in comparison to Ramda, where you need to additionally install @types/ramda.

  • More generic methods

Ramda has an overwhelming list of methods, as one could get lost putting all these methods in one's head. Rambda has smaller method counts and that could be seen as advantage.

Click to see the full list of 107 Ramda methods not implemented in Rambda
  • __
  • addIndex
  • ap
  • aperture
  • apply
  • applyTo
  • ascend
  • binary
  • bind
  • call
  • comparator
  • composeK
  • composeP
  • composeWith
  • construct
  • constructN
  • contains
  • countBy
  • descend
  • differenceWith
  • dissocPath
  • dropLastWhile
  • dropRepeats
  • dropRepeatsWith
  • dropWhile
  • empty
  • eqBy
  • eqProps
  • evolve
  • forEachObjIndexed
  • gt
  • gte
  • hasIn
  • innerJoin
  • insert
  • insertAll
  • into
  • invert
  • invertObj
  • invoker
  • juxt
  • keysIn
  • lift
  • liftN
  • lt
  • lte
  • mapAccum
  • mapAccumRight
  • mapObjIndexed
  • memoizeWith
  • mergeDeepLeft
  • mergeDeepWith
  • mergeDeepWithKey
  • mergeRight
  • mergeWith
  • mergeWithKey
  • move
  • nAry
  • nthArg
  • o
  • objOf
  • of
  • once
  • or
  • otherwise
  • pair
  • partialRight
  • pathSatisfies
  • pickBy
  • pipeK
  • pipeP
  • pipeWith
  • project
  • propSatisfies
  • props
  • reduceBy
  • reduceRight
  • reduceWhile
  • reduced
  • remove
  • scan
  • sequence
  • sortWith
  • splitAt
  • splitWhen
  • symmetricDifferenceWith
  • takeLastWhile
  • takeWhile
  • andThen
  • toPairsIn
  • transduce
  • traverse
  • unapply
  • unary
  • uncurryN
  • unfold
  • union
  • unionWith
  • uniqBy
  • unnest
  • until
  • useWith
  • valuesIn
  • xprod
  • zipWith
  • thunkify
  • default

Install

  • yarn add rambdax

  • For UMD usage either use ./dist/rambdax.umd.js or the following CDN link:

https://unpkg.com/rambdax@CURRENT_VERSION/dist/rambdax.umd.js
  • with deno
import {compose, add} from 'https://raw.githubusercontent.com/selfrefactor/rambdax/master/dist/rambdax.esm.js'

Differences between Rambda and Ramda

  • Rambda's type detects async functions and unresolved Promises. The returned values are 'Async' and 'Promise'.

  • Rambda's type handles NaN input, in which case it returns NaN.

  • Rambda's path and paths accept dot notation - 'x.y' same as ['x','y']

  • Rambda's pick and omit accept comma notation - 'x,y' same as ['x','y']

  • Rambda's map, reject and forEach can iterate over objects not only arrays.

  • Rambda's map and filter pass array index as second argument when mapping over arrays.

  • Rambda's adjust, all, allPass, any, anyPass, findIndex , findLastIndex and reject are passing index as second argument to the predicate function.

  • Rambda's filter returns empty array with bad input(null or undefined), while Ramda throws.

  • Ramda's includes will throw an error if input is neither string nor array, while Rambda version will return false.

  • Ramda's clamp work for letters, while Rambda's method work only for numbers.

If you need more Ramda methods in Rambda, you may either submit a PR or check the extended version of Rambda - Rambdax. In case of the former, you may want to consult with Rambda contribution guidelines.

Benchmarks

Click to expand all benchmark results

There are methods which are benchmarked only with Ramda and Rambda(i.e. no Lodash).

Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.

The benchmarks results are produced from latest versions of Rambda, Lodash(4.17.19) and Ramda(0.27.0).

method Rambda Ramda Lodash
add 96.25% slower 96.24% slower 🚀 Fastest
adjust 🚀 Fastest 5.52% slower 🔳
all 🚀 Fastest 94.95% slower 🔳
allPass 🚀 Fastest 98.95% slower 🔳
any 🚀 Fastest 98.18% slower 6.18% slower
anyPass 🚀 Fastest 99.09% slower 🔳
append 🚀 Fastest 84.09% slower 🔳
applySpec 🚀 Fastest 75.73% slower 🔳
assoc 87.98% slower 57.39% slower 🚀 Fastest
clone 🚀 Fastest 96.03% slower 91.75% slower
compose 🚀 Fastest 96.45% slower 77.83% slower
converge 49.12% slower 🚀 Fastest 🔳
curry 🚀 Fastest 34.9% slower 🔳
curryN 63.32% slower 🚀 Fastest 🔳
defaultTo 🚀 Fastest 50.3% slower 🔳
drop 🚀 Fastest 97.45% slower 🔳
dropLast 🚀 Fastest 97.07% slower 🔳
equals 72.11% slower 79.48% slower 🚀 Fastest
filter 🚀 Fastest 94.74% slower 58.18% slower
find 🚀 Fastest 98.2% slower 88.96% slower
findIndex 🚀 Fastest 97.97% slower 79.39% slower
flatten 6.56% slower 95.38% slower 🚀 Fastest
ifElse 🚀 Fastest 70.97% slower 🔳
includes 🚀 Fastest 71.7% slower 🔳
indexOf 🚀 Fastest 84.08% slower 7.86% slower
init 94.42% slower 97.55% slower 🚀 Fastest
is 🚀 Fastest 11.72% slower 🔳
isEmpty 51.68% slower 93.82% slower 🚀 Fastest
last 🚀 Fastest 99.64% slower 1.05% slower
lastIndexOf 🚀 Fastest 42.38% slower 🔳
map 🚀 Fastest 69.63% slower 4.68% slower
match 🚀 Fastest 46.75% slower 🔳
merge 63.55% slower 🚀 Fastest 55.25% slower
none 🚀 Fastest 98.22% slower 🔳
omit 🚀 Fastest 70.66% slower 97.56% slower
over 🚀 Fastest 50.77% slower 🔳
path 🚀 Fastest 74.94% slower 5.72% slower
pick 🚀 Fastest 26.29% slower 86.82% slower
prop 🚀 Fastest 89.89% slower 🔳
propEq 🚀 Fastest 95.26% slower 🔳
range 95.17% slower 90.22% slower 🚀 Fastest
reduce 52.76% slower 74.02% slower 🚀 Fastest
repeat 85.91% slower 95.31% slower 🚀 Fastest
replace 0.47% slower 28.13% slower 🚀 Fastest
set 🚀 Fastest 36.26% slower 🔳
sort 🚀 Fastest 63.15% slower 🔳
sortBy 🚀 Fastest 61.57% slower 88.88% slower
split 🚀 Fastest 85.34% slower 33.69% slower
splitEvery 🚀 Fastest 90.18% slower 🔳
take 93.44% slower 98.04% slower 🚀 Fastest
takeLast 92.61% slower 98.83% slower 🚀 Fastest
test 🚀 Fastest 94.42% slower 🔳
type 18.91% slower 🚀 Fastest 🔳
uniq 98.98% slower 96.58% slower 🚀 Fastest
update 🚀 Fastest 38.88% slower 🔳
view 🚀 Fastest 82.21% slower 🔳

Used by

API

add

add(a: number, b: number): number

It adds a and b.

R.add(2, 3) // =>  5

Try the above R.add example in Rambda REPL

All Typescript definitions
add(a: number, b: number): number;
add(a: number): (b: number) => number;
Tests
import { add } from './add'

test('with number', () => {
  expect(add(2, 3)).toEqual(5)
  expect(add(7)(10)).toEqual(17)
})

test('string is bad input', () => {
  expect(add('foo', 'bar')).toBeNaN()
})

test('ramda specs', () => {
  expect(add('1', '2')).toEqual(3)
  expect(add(1, '2')).toEqual(3)
  expect(add(true, false)).toEqual(1)
  expect(add(null, null)).toEqual(0)
  expect(add(undefined, undefined)).toEqual(NaN)
  expect(add(new Date(1), new Date(2))).toEqual(3)
})

adjust

adjust<T>(index: number, replaceFn: (x: T) => T, list: ReadonlyArray<T>): T[]

It replaces index in array list with the result of replaceFn(list[i]).

R.adjust(
  0,
  a => a + 1,
  [0, 100]
) // => [1, 100]

Try the above R.adjust example in Rambda REPL

All Typescript definitions
adjust<T>(index: number, replaceFn: (x: T) => T, list: ReadonlyArray<T>): T[];
adjust<T>(index: number, replaceFn: (x: T) => T): (list: ReadonlyArray<T>) => T[];
Tests
import { add } from './add'
import { adjust } from './adjust'
import { pipe } from './pipe'

const list = [ 0, 1, 2 ]
const expected = [ 0, 11, 2 ]

test('happy', () => {})

test('happy', () => {
  expect(adjust(
    1, add(10), list
  )).toEqual(expected)
})

test('with curring type 1 1 1', () => {
  expect(adjust(1)(add(10))(list)).toEqual(expected)
})

test('with curring type 1 2', () => {
  expect(adjust(1)(add(10), list)).toEqual(expected)
})

test('with curring type 2 1', () => {
  expect(adjust(1, add(10))(list)).toEqual(expected)
})

test('with negative index', () => {
  expect(adjust(
    -2, add(10), list
  )).toEqual(expected)
})

test('when index is out of bounds', () => {
  const list = [ 0, 1, 2, 3 ]
  expect(adjust(
    4, add(1), list
  )).toEqual(list)
  expect(adjust(
    -5, add(1), list
  )).toEqual(list)
})

all

all<T>(predicate: (x: T, index: number) => boolean, list: ReadonlyArray<T>): boolean

It returns true, if all members of array list returns true, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > -1

const result = R.all(predicate, arr)
// => true

Try the above R.all example in Rambda REPL

All Typescript definitions
all<T>(predicate: (x: T, index: number) => boolean, list: ReadonlyArray<T>): boolean;
all<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean;
all<T>(predicate: (x: T, index: number) => boolean): (list: ReadonlyArray<T>) => boolean;
all<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => boolean;
Tests
import { all } from './all'

const numArr = [ 0, 1, 2, 3, 4 ]

test('when true', () => {
  const fn = x => x > -1

  expect(all(fn)(numArr)).toBeTrue()
})

test('when false', () => {
  const fn = x => x > 2

  expect(all(fn, numArr)).toBeFalse()
})

test('pass index as second argument', () => {
  const indexes = []
  const fn = (x, i) => {
    indexes.push(i)

    return x > 5
  }
  all(fn, [ 10, 12, 14 ])

  expect(indexes).toEqual([ 0, 1, 2 ])
})

allFalse

allFalse(...inputs: any[]): boolean

It returns true if all inputs arguments are falsy(empty objects and empty arrays are considered falsy).

Functions are valid inputs, but these functions cannot have their own arguments.

This method is very similar to R.anyFalse, R.anyTrue and R.allTrue

R.allFalse(0, null, [], {}, '', () => false)
// => true

Try the above R.allFalse example in Rambda REPL

All Typescript definitions
allFalse(...inputs: any[]): boolean;
Tests
import { runTests } from 'helpers-fn'

import { allFalse } from './allFalse'

const happy = { ok : [ () => false, () => [], () => {}, null, false, [] ] }
const withArray = { fail : [ ...happy.ok, [ 1 ] ] }
const withObject = { fail : [ ...happy.ok, { a : 1 } ] }
const withFunction = { fail : [ ...happy.ok, () => ({ a : 1 }) ] }
const withBoolean = { fail : [ ...happy.ok, true ] }

const testData = {
  label : 'R.allFalse',
  data  : [ happy, withArray, withObject, withFunction, withBoolean ],
  fn    : input => allFalse(...input),
}
runTests(testData)

allPass

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It returns true, if all functions of predicates return true, when input is their argument.

const input = {
  a : 1,
  b : 2,
}
const predicates = [
  x => x.a === 1,
  x => x.b === 2,
]
const result = R.allPass(predicates)(input) // => true

Try the above R.allPass example in Rambda REPL

All Typescript definitions
allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean;
Tests
import { allPass } from './allPass'

test('happy', () => {
  const rules = [ x => typeof x === 'number', x => x > 10, x => x * 7 < 100 ]

  expect(allPass(rules)(11)).toBeTrue()

  expect(allPass(rules)(undefined)).toBeFalse()
})

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 2 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeTrue()
})

test('when returns false', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 3 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeFalse()
})

allTrue

allTrue(...input: any[]): boolean

It returns true if all inputs arguments are truthy(empty objects and empty arrays are considered falsy).

R.allTrue(1, true, {a: 1}, [1], 'foo', () => true)
// => true

Try the above R.allTrue example in Rambda REPL

All Typescript definitions
allTrue(...input: any[]): boolean;
Tests
import { allTrue } from './allTrue'

test('with functions', () => {
  const foo = () => 1
  const bar = () => false
  const baz = () => JSON.parse('{sda')
  const result = allTrue(
    foo, bar, baz
  )
  expect(result).toBeFalse()
})

test('usage with non boolean', () => {
  const foo = { a : 1 }
  const baz = [ 1, 2, 3 ]

  const result = allTrue(
    foo, foo, baz
  )
  expect(result).toBeTrue()
})

test('usage with boolean', () => {
  const foo = 4
  const baz = [ 1, 2, 3 ]

  const result = allTrue(foo > 2, baz.length === 3)
  expect(result).toBeTrue()
})

test('escapes early - case 0', () => {
  const foo = undefined
  const result = allTrue(foo, () => foo.a)
  expect(result).toBeFalse()
})

test('escapes early - case 1', () => {
  const foo = null
  const result = allTrue(foo, () => foo.a)
  expect(result).toBeFalse()
})

test('escapes early - case 2', () => {
  const foo = { a : 'bar' }
  const result = allTrue(
    foo, foo.a, foo.a.b
  )
  expect(result).toBeFalse()
})

test('escapes early - case 3', () => {
  const foo = { a : { b : 'foo' } }
  const result = allTrue(
    foo,
    () => foo.a,
    () => foo.a.b
  )
  expect(result).toBeTrue()
})

allType

allType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if all of its inputs arguments belong to targetType.

const targetType = 'String'

const result = R.allType(
  targetType
)('foo', 'bar', 'baz')
// => true

Try the above R.allType example in Rambda REPL

All Typescript definitions
allType(targetType: RambdaTypes): (...input: any[]) => boolean;
Tests
import { allType } from './allType'

test('when true', () => {
  const result = allType('Array')(
    [ 1, 2, 3 ], [], [ null ]
  )

  expect(result).toBeTrue()
})

test('when false', () => {
  const result = allType('String')(
    1, undefined, null, []
  )

  expect(result).toBeFalse()
})

always

always<T>(x: T): () => T

It returns function that always returns x.

const fn = R.always(7)

console.log(fn())// => 7

Try the above R.always example in Rambda REPL

All Typescript definitions
always<T>(x: T): () => T;
Tests
import { always } from './always'
import { F } from './F'

test('happy', () => {
  const fn = always(7)

  expect(fn()).toEqual(7)
  expect(fn()).toEqual(7)
})

test('f', () => {
  const fn = always(F())

  expect(fn()).toBeFalse()
  expect(fn()).toBeFalse()
})

and

and<T extends { and?: ((...a: readonly any[]) => any)

Returns true if both arguments are true. Otherwise, it returns false.

R.and(true, true); // => true
R.and(false, true); // => false

Try the above R.and example in Rambda REPL

All Typescript definitions
and<T extends { and?: ((...a: readonly any[]) => any); } | number | boolean | string | null>(fn1: T, val2: any): boolean;
and<T extends { and?: ((...a: readonly any[]) => any); } | number | boolean | string | null>(fn1: T): (val2: any) => boolean;
Tests
import { and } from './and'

test('happy', () => {
  expect(and(true, true)).toBeTrue()
  expect(and(true)(true)).toBeTrue()
  expect(and(4)(2)).toBe(2)
  expect(and(true, false)).toBeFalse()
  expect(and(false, true)).toBeFalse()
  expect(and(false, false)).toBeFalse()
})

any

any<T>(predicate: (x: T, i: number) => boolean, list: ReadonlyArray<T>): boolean

It returns true, if at least one member of list returns true, when passed to predicate function.

const list = [1, 2, 3]
const predicate = x => x * x > 8
R.any(fn, list)
// => true

Try the above R.any example in Rambda REPL

All Typescript definitions
any<T>(predicate: (x: T, i: number) => boolean, list: ReadonlyArray<T>): boolean;
any<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean;
any<T>(predicate: (x: T, i: number) => boolean): (list: ReadonlyArray<T>) => boolean;
any<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => boolean;
Tests
import { any } from './any'

const arr = [ 1, 2 ]

test('no curry', () => {
  expect(any(val => val < 0, arr)).toBeFalse()
})

test('with curry', () => {
  expect(any(val => val < 2)(arr)).toBeTrue()
})

test('passes index to predicate', () => {
  any((x, i) => {
    expect(typeof x).toBe('string')
    expect(typeof i).toBe('number')
  })([ 'foo', 'bar' ])
})

anyFalse

anyFalse(...input: any[]): boolean

It returns true if any of inputs is falsy(empty objects and empty arrays are considered falsy).

R.anyFalse(1, {a: 1}, [1], () => false)
// => true

Try the above R.anyFalse example in Rambda REPL

All Typescript definitions
anyFalse(...input: any[]): boolean;
Tests
import { anyFalse } from './anyFalse'

test('when true', () => {
  expect(anyFalse(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyFalse(true, true)).toBeFalsy()
})

test('supports function', () => {
  expect(anyFalse(
    true,
    () => true,
    () => false
  )).toBeTruthy()
})

anyPass

anyPass<T>(predicates: ReadonlyArray<SafePred<T>>): SafePred<T>

It accepts list of predicates and returns a function. This function with its input will return true, if any of predicates returns true for this input.

const isBig = x => x > 20
const isOdd = x => x % 2 === 1
const input = 11

const fn = R.anyPass(
  [isBig, isOdd]
)

const result = fn(input) 
// => true

Try the above R.anyPass example in Rambda REPL

All Typescript definitions
anyPass<T>(predicates: ReadonlyArray<SafePred<T>>): SafePred<T>;
Tests
import { anyPass } from './anyPass'

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]
  const predicate = anyPass(rules)
  expect(predicate('foo')).toBeTrue()
  expect(predicate(6)).toBeFalse()
})

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]

  expect(anyPass(rules)(11)).toBeTrue()

  expect(anyPass(rules)(undefined)).toBeFalse()
})

const obj = {
  a : 1,
  b : 2,
}

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.a === 2 ]

  expect(anyPass(conditionArr)(obj)).toBeTrue()
})

test('when returns false + curry', () => {
  const conditionArr = [ val => val.a === 2, val => val.b === 3 ]

  expect(anyPass(conditionArr)(obj)).toBeFalse()
})

test('happy', () => {
  expect(anyPass([])(3)).toEqual(false)
})

anyTrue

anyTrue(...input: any[]): boolean

It returns true if any of inputs arguments are truthy(empty objects and empty arrays are considered falsy).

R.anyTrue(0, null, [], {}, '', () => true)
// => true

Try the above R.anyTrue example in Rambda REPL

All Typescript definitions
anyTrue(...input: any[]): boolean;
Tests
import { anyTrue } from './anyTrue'

test('when true', () => {
  expect(anyTrue(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyTrue(
    false, false, false
  )).toBeFalsy()
})

test('supports function', () => {
  expect(anyTrue(
    false,
    false,
    false,
    () => false,
    () => true
  )).toBeTruthy()
})

anyType

anyType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if at least one of its inputs arguments belongs to targetType.

targetType is one of the possible returns of R.type

const targetType = 'String'

const result = R.anyType(
  targetType
)(1, {}, 'foo')
// => true

Try the above R.anyType example in Rambda REPL

All Typescript definitions
anyType(targetType: RambdaTypes): (...input: any[]) => boolean;
Tests
import { anyType } from './anyType'

test('when true', () => {
  const result = anyType('Array')(
    1, undefined, null, []
  )

  expect(result).toBeTrue()
})

test('when false', () => {
  const result = anyType('String')(
    1, undefined, null, []
  )

  expect(result).toBeFalse()
})

append

append<T>(x: T, listOrString: ReadonlyArray<T>): T[]

It adds element x at the end of listOrString.

const x = 'foo'

const result = [
  R.append(x, 'cherry_'),
  R.append(x, ['bar', 'baz'])
]
// => ['cherry_foo', ['bar', 'baz', 'foo']]

Try the above R.append example in Rambda REPL

All Typescript definitions
append<T>(x: T, listOrString: ReadonlyArray<T>): T[];
append<T>(x: T): <T>(listOrString: ReadonlyArray<T>) => T[];
Tests
import { append } from './append'
import { compose } from './compose'
import { flatten } from './flatten'
import { map } from './map'

test('with strings', () => {
  expect(append('o', 'fo')).toEqual('foo')
})

test('with arrays', () => {
  expect(append('tests', [ 'write', 'more' ])).toEqual([
    'write',
    'more',
    'tests',
  ])
})

test('append to empty array', () => {
  expect(append('tests', [])).toEqual([ 'tests' ])
})

test('happy', () => {
  const result = compose(flatten, map(append(0)))([ [ 1 ], [ 2 ], [ 3 ] ])
  expect(result).toEqual([ 1, 0, 2, 0, 3, 0 ])
})

test('should not modify arguments', () => {
  const a = [ 1, 2, 3 ]
  const b = append(4, a)

  expect(a).toEqual([ 1, 2, 3 ])
  expect(b).toEqual([ 1, 2, 3, 4 ])
})

applySpec

applySpec<Spec extends Record<string, (...args: readonly any[]) => any>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }

It returns a curried function with the same arity as the longest function in the spec object. Arguments will be applied to the spec methods recursively.

const spec = {
  name: R.path('deeply.nested.firstname')
}
const json = {
  deeply: {
   nested: {
      firstname: 'barry'
    }
  }
}
const result = R.applySpec(spec, json) // => { name: 'barry' }

// Second example
const getMetrics = R.applySpec({
  sum: R.add,
  nested: { mul: R.multiply }
})
getMetrics(2, 4) 
// => { sum: 6, nested: { mul: 8 } }

Try the above R.applySpec example in Rambda REPL

All Typescript definitions
applySpec<Spec extends Record<string, (...args: readonly any[]) => any>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> };
applySpec<T>(spec: any): (...args: readonly any[]) => T;
Tests
import { applySpec as applySpecRamda, nAry } from 'ramda'

import { add, always, compose, dec, inc, map, path, prop, T } from '../rambda'
import { applySpec } from './applySpec'

test('different than Ramda when bad spec', () => {
  const result = applySpec({ sum : { a : 1 } })(1, 2)
  const ramdaResult = applySpecRamda({ sum : { a : 1 } })(1, 2)
  expect(result).toEqual({})
  expect(ramdaResult).toEqual({ sum : { a : {} } })
})

test('works with empty spec', () => {
  expect(applySpec({})()).toEqual({})
  expect(applySpec([])(1, 2)).toEqual({})
  expect(applySpec(null)(1, 2)).toEqual({})
})

test('works with unary functions', () => {
  const result = applySpec({
    v : inc,
    u : dec,
  })(1)
  const expected = {
    v : 2,
    u : 0,
  }
  expect(result).toEqual(expected)
})

test('works with binary functions', () => {
  const result = applySpec({ sum : add })(1, 2)
  expect(result).toEqual({ sum : 3 })
})

test('works with nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : { sum : add },
  })(1, 2)
  const expected = {
    unnested : 0,
    nested   : { sum : 3 },
  }
  expect(result).toEqual(expected)
})

test('works with arrays of nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : [ { sum : add } ],
  })(1, 2)

  expect(result).toEqual({
    unnested : 0,
    nested   : [ { sum : 3 } ],
  })
})

test('works with arrays of spec objects', () => {
  const result = applySpec([ { sum : add } ])(1, 2)

  expect(result).toEqual([ { sum : 3 } ])
})

test('works with arrays of functions', () => {
  const result = applySpec([ map(prop('a')), map(prop('b')) ])([
    {
      a : 'a1',
      b : 'b1',
    },
    {
      a : 'a2',
      b : 'b2',
    },
  ])
  const expected = [
    [ 'a1', 'a2' ],
    [ 'b1', 'b2' ],
  ]
  expect(result).toEqual(expected)
})

test('works with a spec defining a map key', () => {
  expect(applySpec({ map : prop('a') })({ a : 1 })).toEqual({ map : 1 })
})

test.skip('retains the highest arity', () => {
  const f = applySpec({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  expect(f.length).toBe(5)
})

test('returns a curried function', () => {
  expect(applySpec({ sum : add })(1)(2)).toEqual({ sum : 3 })
})

// Additional tests
// ============================================
test('arity', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(
    spec, 1, 2, 3
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('arity over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(
    spec, 1, 2, 3, 4, 5
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('curried', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(spec)(1)(2)(3)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('curried over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('undefined property', () => {
  const spec = { prop : path([ 'property', 'doesnt', 'exist' ]) }
  expect(applySpec(spec, {})).toEqual({ prop : undefined })
})

test('restructure json object', () => {
  const spec = {
    id          : path('user.id'),
    name        : path('user.firstname'),
    profile     : path('user.profile'),
    doesntExist : path('user.profile.doesntExist'),
    info        : { views : compose(inc, prop('views')) },
    type        : always('playa'),
  }

  const data = {
    user : {
      id        : 1337,
      firstname : 'john',
      lastname  : 'shaft',
      profile   : 'shaft69',
    },
    views : 42,
  }

  expect(applySpec(spec, data)).toEqual({
    id          : 1337,
    name        : 'john',
    profile     : 'shaft69',
    doesntExist : undefined,
    info        : { views : 43 },
    type        : 'playa',
  })
})

assoc

assoc<T, U, K extends string>(prop: K, newValue: T, obj: U): Record<K, T> & U

It makes a shallow clone of obj with setting or overriding the property prop with newValue.

R.assoc('c', 3, {a: 1, b: 2})
//=> {a: 1, b: 2, c: 3}

Try the above R.assoc example in Rambda REPL

All Typescript definitions
assoc<T, U, K extends string>(prop: K, newValue: T, obj: U): Record<K, T> & U;
assoc<T, K extends string>(prop: K, newValue: T): <U>(obj: U) => Record<K, T> & U;
assoc<K extends string>(prop: K): <T, U>(newValue: T, obj: U) => Record<K, T> & U;
Tests
import { assoc } from './assoc'

test('adds a key to an empty object', () => {
  expect(assoc(
    'a', 1, {}
  )).toEqual({ a : 1 })
})

test('adds a key to a non-empty object', () => {
  expect(assoc(
    'b', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assoc('b', 2)({ a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assoc('b')(2, { a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assoc('b')(2)({ a : 1 })

  expect(result).toEqual({
    a : 1,
    b : 2,
  })
})

test('changes an existing key', () => {
  expect(assoc(
    'a', 2, { a : 1 }
  )).toEqual({ a : 2 })
})

test('undefined is considered an empty object', () => {
  expect(assoc(
    'a', 1, undefined
  )).toEqual({ a : 1 })
})

test('null is considered an empty object', () => {
  expect(assoc(
    'a', 1, null
  )).toEqual({ a : 1 })
})

test('value can be null', () => {
  expect(assoc(
    'a', null, null
  )).toEqual({ a : null })
})

test('value can be undefined', () => {
  expect(assoc(
    'a', undefined, null
  )).toEqual({ a : undefined })
})

test('assignment is shallow', () => {
  expect(assoc(
    'a', { b : 2 }, { a : { c : 3 } }
  )).toEqual({ a : { b : 2 } })
})

assocPath

assocPath<T, U>(path: Path, newValue: T, obj: U): U

It makes a shallow clone of obj with setting or overriding with newValue the property found with path.

const path = 'b.c'
const newValue = 2
const obj = { a: 1 }

R.assocPath(path, newValue, obj)
// => { a : 1, b : { c : 2 }}

Try the above R.assocPath example in Rambda REPL

All Typescript definitions
assocPath<T, U>(path: Path, newValue: T, obj: U): U;
assocPath<T, U>(path: Path, newValue: T): (obj: U) => U;
assocPath<T, U>(path: Path): FunctionToolbelt.Curry<(newValue: T, obj: U) => U>;
Tests
import { assocPath } from './assocPath'

test('adds a key to an empty object', () => {
  expect(assocPath(
    [ 'a' ], 1, {}
  )).toEqual({ a : 1 })
})

test('adds a key to a non-empty object', () => {
  expect(assocPath(
    'b', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object', () => {
  expect(assocPath(
    'b.c', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a nested key to a nested non-empty object - curry case 1', () => {
  expect(assocPath('b.d',
    3)({
    a : 1,
    b : { c : 2 },
  })).toEqual({
    a : 1,
    b : {
      c : 2,
      d : 3,
    },
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assocPath('b', 2)({ a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object - curry case 1', () => {
  expect(assocPath('b.c', 2)({ a : 1 })).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a nested array to a non-empty object - curry case 1', () => {
  expect(assocPath('b.0', 2)({ a : 1 })).toEqual({
    a : 1,
    b : [ 2 ],
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assocPath('b')(2, { a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assocPath('b')(2)({ a : 1 })

  expect(result).toEqual({
    a : 1,
    b : 2,
  })
})

test('changes an existing key', () => {
  expect(assocPath(
    'a', 2, { a : 1 }
  )).toEqual({ a : 2 })
})

test('undefined is considered an empty object', () => {
  expect(assocPath(
    'a', 1, undefined
  )).toEqual({ a : 1 })
})

test('null is considered an empty object', () => {
  expect(assocPath(
    'a', 1, null
  )).toEqual({ a : 1 })
})

test('value can be null', () => {
  expect(assocPath(
    'a', null, null
  )).toEqual({ a : null })
})

test('value can be undefined', () => {
  expect(assocPath(
    'a', undefined, null
  )).toEqual({ a : undefined })
})

test('assignment is shallow', () => {
  expect(assocPath(
    'a', { b : 2 }, { a : { c : 3 } }
  )).toEqual({ a : { b : 2 } })
})

test('empty array as path', () => {
  const result = assocPath(
    [], 3, {
      a : 1,
      b : 2,
    }
  )
  expect(result).toEqual(3)
})

test('happy', () => {
  const expected = { foo : { bar : { baz : 42 } } }
  const result = assocPath(
    [ 'foo', 'bar', 'baz' ], 42, { foo : null }
  )
  expect(result).toEqual(expected)
})

both

both(pred1: Pred, pred2: Pred): Pred

It returns a function with input argument.

This function will return true, if both firstCondition and secondCondition return true when input is passed as their argument.

const firstCondition = x => x > 10
const secondCondition = x => x < 20
const fn = R.both(secondCondition)

const result = [fn(15), fn(30)]
// => [true, false]

Try the above R.both example in Rambda REPL

All Typescript definitions
both(pred1: Pred, pred2: Pred): Pred;
both<T>(pred1: Predicate<T>, pred2: Predicate<T>): Predicate<T>;
both<T>(pred1: Predicate<T>): (pred2: Predicate<T>) => Predicate<T>;
both(pred1: Pred): (pred2: Pred) => Pred;
Tests
import { both } from './both'

const firstFn = val => val > 0
const secondFn = val => val < 10

test('with curry', () => {
  expect(both(firstFn)(secondFn)(17)).toBeFalse()
})

test('without curry', () => {
  expect(both(firstFn, secondFn)(7)).toBeTrue()
})

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = both(between, total20)
  expect(fn(
    5, 7, 8
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return false
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  both(F, Z)()

  expect(effect).toBe('not evaluated')
})

chain

chain<T, U>(fn: (n: T) => readonly U[], list: readonly T[]): U[]

The method is also known as flatMap.

const duplicate = n => [ n, n ]
const list = [ 1, 2, 3 ]

const result = chain(duplicate, list)
// => [ 1, 1, 2, 2, 3, 3 ]

Try the above R.chain example in Rambda REPL

All Typescript definitions
chain<T, U>(fn: (n: T) => readonly U[], list: readonly T[]): U[];
chain<T, U>(fn: (n: T) => readonly U[]): (list: readonly T[]) => U[];
chain<X0, X1, R>(fn: (x0: X0, x1: X1) => R, fn1: (x1: X1) => X0): (x1: X1) => R;
Tests
import { chain } from './chain'

const duplicate = n => [ n, n ]

test('happy', () => {
  const fn = x => [ x * 2 ]
  const list = [ 1, 2, 3 ]

  const result = chain(fn, list)

  expect(result).toEqual([ 2, 4, 6 ])
})

test('maps then flattens one level', () => {
  expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('maps then flattens one level - curry', () => {
  expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('flattens only one level', () => {
  const nest = n => [ [ n ] ]
  expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])
})

change

change<T>(
  origin: object,
  path: string,
  changeData: any
): T

It helps changing object's properties if there are below 3 levels deep.

It is intended for usage inside unit tests, when you need more powerful method to change object's properties.

path input argument allows you to specify which object's sub-branch you want to focus on. You must pass an empty string if you target the whole origin object.

changeData can be a direct value or an object. If it is a object, then this object is used to edit or add new properties to the selected sub-branch.

const result = R.change(
  { a: 1, b: { c: 2 } },
  'b.c',
  10
)
const expected = {
  a: 1,
  b: { c: 10 }
}
// => `result` is equal to `expected`

const origin = {
  foo : 1,
  bar : { nested : 2 },
}
const changeData = {
  bar : { a : 3 },
  baz : 4,
}
const complexResult = R.change(
  origin, '', changeData
)

const complexExpected = {
  foo : 1,
  bar : {
    a : 3,
    nested : 2,
  },
  baz: 4
}
// => `complexResult` is equal to `complexExpected`

Try the above R.change example in Rambda REPL

All Typescript definitions
change<T>(
  origin: object,
  path: string,
  changeData: any
): T;
change<Input, Output>(
  origin: Input,
  path: string,
  changeData: any
): Output;
Tests
import { change } from './change'

test('happy', () => {
  const localOrigin = {
    foo : 1,
    bar : { nested : 2 },
  }
  const changeData = {
    bar : { a : 3 },
    baz : 4,
  }
  const result = change(
    localOrigin, '', changeData
  )

  const expected = {
    foo : 1,
    bar : {
      a      : 3,
      nested : 2,
    },
    baz : 4,
  }

  expect(result).toEqual(expected)
})

const origin = {
  a   : 0,
  foo : {
    bar : 1,
    baz : false,
    bax : { nested : 2 },
  },
  first : {
    second : {
      third : {
        fourthA : 3,
        fourthB : 4,
        fourth  : {
          a     : 1,
          fifth : { unreachable : 22 },
        },
      },
    },
  },
}

test('when rule is not an object', () => {
  const result = change(
    origin, 'foo.bax.nested', 7
  )
  const expected = {
    a   : 0,
    foo : {
      bar : 1,
      baz : false,
      bax : { nested : 7 },
    },
    first : origin.first,
  }

  expect(result).toEqual(expected)
})

test('works with 4 levels deep nesting', () => {
  const changeData = {
    foo : {
      bar : 7,
      bax : { bay : 8 },
    },
    first : {
      second : {
        b     : 7,
        third : {
          fourthA : 9,
          // This is 5th level nesting
          // so we will receive a full change property
          // instead of merge
          ///////////////////////////
          fourth  : { a : 2 },
        },
      },
    },
  }
  const result = change(
    origin, '', changeData
  )
  const expected = {
    a   : 0,
    foo : {
      bar : 7,
      baz : false,
      bax : {
        nested : 2,
        bay    : 8,
      },
    },
    first : {
      second : {
        third : {
          fourthA : 9,
          fourthB : 4,
          fourth  : { a : 2 },
        },
        b : 7,
      },
    },
  }
  expect(result).toEqual(expected)
})

clamp

clamp(min: number, max: number, input: number): number

Restrict a number input to be withing min and max limits.

If input is bigger than max, then the result is max.

If input is smaller than min, then the result is min.

R.clamp(0, 10, 5) //=> 5
R.clamp(0, 10, -1) //=> 0
R.clamp(0, 10, 11) //=> 10

Try the above R.clamp example in Rambda REPL

All Typescript definitions
clamp(min: number, max: number, input: number): number;
clamp(min: number, max: number): (input: number) => number;
Tests
import { clamp } from './clamp'

test('when min is greater than max', () => {
  expect(() => clamp(
    -5, -10, 5
  )).toThrowWithMessage(Error,
    'min must not be greater than max in clamp(min, max, value)')
})

test('rambda specs', () => {
  expect(clamp(
    1, 10, 0
  )).toEqual(1)
  expect(clamp(
    3, 12, 1
  )).toEqual(3)
  expect(clamp(
    -15, 3, -100
  )).toEqual(-15)
  expect(clamp(
    1, 10, 20
  )).toEqual(10)
  expect(clamp(
    3, 12, 23
  )).toEqual(12)
  expect(clamp(
    -15, 3, 16
  )).toEqual(3)
  expect(clamp(
    1, 10, 4
  )).toEqual(4)
  expect(clamp(
    3, 12, 6
  )).toEqual(6)
  expect(clamp(
    -15, 3, 0
  )).toEqual(0)
})

clone

clone<T>(input: T): T

It creates a deep copy of the input, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.

const objects = [{a: 1}, {b: 2}];
const objectsClone = R.clone(objects);

const result = [
  R.equals(objects, objectsClone),
  R.equals(objects[0], objectsClone[0]),
] // => [ true, true ]

Try the above R.clone example in Rambda REPL

All Typescript definitions
clone<T>(input: T): T;
clone<T>(input: ReadonlyArray<T>): T[];
Tests
import assert from 'assert'

import { clone } from './clone'
import { equals } from './equals'

test('with array', () => {
  const arr = [
    {
      b : 2,
      c : 'foo',
      d : [ 1, 2, 3 ],
    },
    1,
    new Date(),
    null,
  ]
  expect(clone(arr)).toEqual(arr)
})

test('with object', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
    d : [ 1, 2, 3 ],
    e : new Date(),
  }
  expect(clone(obj)).toEqual(obj)
})

test('with date', () => {
  const date = new Date(
    2014, 10, 14, 23, 59, 59, 999
  )

  const cloned = clone(date)
  assert.notStrictEqual(date, cloned)
  expect(cloned).toEqual(new Date(
    2014, 10, 14, 23, 59, 59, 999
  ))

  expect(cloned.getDay()).toEqual(5)
})

test('with R.equals', () => {
  const objects = [ { a : 1 }, { b : 2 } ]

  const objectsClone = clone(objects)

  const result = [
    equals(objects, objectsClone),
    equals(objects[ 0 ], objectsClone[ 0 ]),
  ]
  expect(result).toEqual([ true, true ])
})

compact

compact<T>(x: any[]): T[]

It returns a clone of list without the falsy or empty elements.

const list = [null, '', {}, [], 1]

const result = R.compact(list)
// => [1]

Try the above R.compact example in Rambda REPL

All Typescript definitions
compact<T>(x: any[]): T[];
Tests
import { compact } from './compact'

test('happy', () => {
  const arr = [
    1,
    null,
    undefined,
    false,
    '',
    ' ',
    () => {},
    'foo',
    {},
    [],
    [ 1 ],
    /\s/g,
  ]

  const result = compact(arr)
  const expected = [ 1, false, ' ', 'foo', [ 1 ] ]

  expect(result).toEqual(expected)
})

complement

complement(pred: (...args: any[]) => boolean): (...args: any[]) => boolean

It returns inverted version of origin function that accept input as argument.

The return value of inverted is the negative boolean value of origin(input).

const origin = x => x > 5
const inverted = complement(origin)

const result = [
  origin(7),
  inverted(7)
] => [ true, false ]

Try the above R.complement example in Rambda REPL

All Typescript definitions
complement(pred: (...args: any[]) => boolean): (...args: any[]) => boolean;
Tests
import { complement } from './complement'

test('happy', () => {
  const fn = complement(x => x.length === 0)

  expect(fn([ 1, 2, 3 ])).toBeTrue()
})

test('with multiple parameters', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const f = complement(between)
  expect(f(
    4, 5, 11
  )).toEqual(false)
  expect(f(
    12, 2, 6
  )).toEqual(true)
})

compose

compose<T1>(fn0: () => T1): () => T1

It performs right-to-left function composition.

const result = R.compose(
  R.map(x => x * 2),
  R.filter(x => x > 2)
)([1, 2, 3, 4])

// => [6, 8]

Try the above R.compose example in Rambda REPL

All Typescript definitions
compose<T1>(fn0: () => T1): () => T1;
compose<V0, T1>(fn0: (x0: V0) => T1): (x0: V0) => T1;
compose<V0, V1, T1>(fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T1;
compose<V0, V1, V2, T1>(fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T1;

compose<T1, T2>(fn1: (x: T1) => T2, fn0: () => T1): () => T2;
compose<V0, T1, T2>(fn1: (x: T1) => T2, fn0: (x0: V0) => T1): (x0: V0) => T2;
compose<V0, V1, T1, T2>(fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T2;
compose<V0, V1, V2, T1, T2>(fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T2;

compose<T1, T2, T3>(fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: () => T1): () => T3;
compose<V0, T1, T2, T3>(fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x: V0) => T1): (x: V0) => T3;
compose<V0, V1, T1, T2, T3>(fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T3;
compose<V0, V1, V2, T1, T2, T3>(fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T3;

compose<T1, T2, T3, T4>(fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: () => T1): () => T4;
compose<V0, T1, T2, T3, T4>(fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x: V0) => T1): (x: V0) => T4;
compose<V0, V1, T1, T2, T3, T4>(fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T4;
compose<V0, V1, V2, T1, T2, T3, T4>(fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T4;

compose<T1, T2, T3, T4, T5>(fn4: (x: T4) => T5, fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: () => T1): () => T5;
compose<V0, T1, T2, T3, T4, T5>(fn4: (x: T4) => T5, fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x: V0) => T1): (x: V0) => T5;
compose<V0, V1, T1, T2, T3, T4, T5>(fn4: (x: T4) => T5, fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T5;
compose<V0, V1, V2, T1, T2, T3, T4, T5>(fn4: (x: T4) => T5, fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T5;

compose<T1, T2, T3, T4, T5, T6>(fn5: (x: T5) => T6, fn4: (x: T4) => T5, fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: () => T1): () => T6;
compose<V0, T1, T2, T3, T4, T5, T6>(fn5: (x: T5) => T6, fn4: (x: T4) => T5, fn3: (x: T3) => T4, fn2: (x: T2) => T3, fn1: (x: T1) => T2, fn0: (x: V0) => T1): (x: V0) => T6;
compose<V0, V1, T1, T2, T3, T4, T5, T6>(
  fn5: (x: T5) => T6,
  fn4: (x: T4) => T5,
  fn3: (x: T3) => T4,
  fn2: (x: T2) => T3,
  fn1: (x: T1) => T2,
  fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T6;
compose<V0, V1, V2, T1, T2, T3, T4, T5, T6>(
  fn5: (x: T5) => T6,
  fn4: (x: T4) => T5,
  fn3: (x: T3) => T4,
  fn2: (x: T2) => T3,
  fn1: (x: T1) => T2,
  fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T6;
Tests
import { add } from './add'
import { compose } from './compose'
import { filter } from './filter'
import { last } from './last'
import { map } from './map'

test('happy', () => {
  const result = compose(
    last, map(add(10)), map(add(1))
  )([ 1, 2, 3 ])

  expect(result).toEqual(14)
})

test('can accepts initially two arguments', () => {
  const result = compose(map(x => x * 2),
    (list, limit) => filter(x => x > limit, list))([ 1, 2, 3, 4, false ], 2)

  expect(result).toEqual([ 6, 8 ])
})

test('when no arguments is passed', () => {
  expect(() => compose()).toThrow('compose requires at least one argument')
})

test('ramda spec', () => {
  const f = function (
    a, b, c
  ){
    return [ a, b, c ]
  }
  const g = compose(f)

  expect(g(
    1, 2, 3
  )).toEqual([ 1, 2, 3 ])
})

composeAsync

composeAsync<Out>(
  ...fns: (Async<any> | Func<any>)[]
): (input: any) => Promise<Out>

Asynchronous version of R.compose

const add = async x => {
  await R.delay(500)
  return x + 1
}
const passOn = async x => fn(x)

const result = R.composeAsync(
  add,
  passOn
)(0)
// `result` resolves to `2`

Try the above R.composeAsync example in Rambda REPL

All Typescript definitions
composeAsync<Out>(
  ...fns: (Async<any> | Func<any>)[]
): (input: any) => Promise<Out>;
composeAsync<Out>(
  ...fns: (Async<any> | Func<any>)[]
): (input: any) => Promise<Out>;
Tests
import { composeAsync } from './composeAsync'
import { delay as delayModule } from './delay'
import { equals } from './equals'
import { map } from './map'
import { mapAsync } from './mapAsync'
import { prop } from './prop'
import { tapAsync } from './tapAsync'

test('1', async () => {
  const fn = input =>
    new Promise(resolve => {
      setTimeout(() => {
        resolve({
          type    : 'result',
          payload : input,
        })
      }, 100)
    })

  const list = [ 'foo', 'bar' ].map(a => fn(a))

  const result = await composeAsync(
    map(prop('payload')),
    async inputs => Promise.all(inputs.map(async input => fn(input))),
    map(prop('payload'))
  )(await Promise.all(list))

  expect(result).toEqual([ 'foo', 'bar' ])
})

test('2', async () => {
  const delay = ms =>
    new Promise(resolve => {
      setTimeout(() => {
        resolve(ms + 110)
      }, ms)
    })

  const delayAsync = async ms => delay(ms)

  const result = await composeAsync(
    a => a - 1000,
    a => a,
    async a => delayAsync(a),
    a => a + 11
  )(await delay(20))
  expect(result).toEqual(-749)
})

test('3', async () => {
  try {
    const delay = ms =>
      new Promise((_, reject) => {
        setTimeout(() => {
          reject('error')
        }, ms)
      })

    const delayAsync = async ms => delay(ms)

    await composeAsync(a => a - 1000, delayAsync)(20)
  } catch (err){
    expect(err).toEqual('error')
  }
})

test('4', async () => {
  let sideEffect
  const result = await composeAsync(tapAsync(async x => {
    sideEffect = equals(x, [ 2, 4, 6 ])

    return delayModule(x * 3)
  }),
  mapAsync(async x => {
    await delayModule(x * 100)

    return x * 2
  }))([ 1, 2, 3 ])

  expect(result).toEqual([ 2, 4, 6 ])

  expect(sideEffect).toEqual(true)
})

test('inside compose explicit `async` keyword', async () => {
  const delay = ms =>
    new Promise((res, rej) => {
      const b = ms + 7

      res(b)
    })

  const result = await composeAsync(
    a => a,
    a => a + 1000,
    async a => delay(a),
    a => a + 11
  )(20)

  expect(result).toEqual(1038)
})

const delayFn = ms =>
  new Promise((res, rej) => {
    const b = ms + 7

    res(b)
  })

test('known issue - function returning promise', async () => {
  const result = await composeAsync(
    a => a,
    a => a + 1000,
    delayFn,
    a => a + 11
  )(20)

  expect(result).toEqual('[object Promise]1000')
})

test('throw error', async () => {
  const delay = async () => {
    await delayFn(1)
    JSON.parse('{foo')
  }

  let flag = true
  try {
    await composeAsync(
      a => a,
      a => a + 1000,
      async () => delay(),
      a => a + 11
    )(20)
  } catch (e){
    flag = false
  }

  expect(flag).toBeFalse()
})

concat

concat<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[]

It returns a new string or array, which is the result of merging x and y.

R.concat([1, 2])([3, 4]) // => [1, 2, 3, 4]
R.concat('foo', 'bar') // => 'foobar'

Try the above R.concat example in Rambda REPL

All Typescript definitions
concat<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[];
concat<T>(x: ReadonlyArray<T>): (y: ReadonlyArray<T>) => T[];
concat(x: string, y: string): string;
concat(x: string): (y: string) => string;
Tests
import { concat } from './concat'

test('happy', () => {
  const arr1 = [ 'a', 'b', 'c' ]
  const arr2 = [ 'd', 'e', 'f' ]

  const a = concat(arr1, arr2)
  const b = concat(arr1)(arr2)
  const expectedResult = [ 'a', 'b', 'c', 'd', 'e', 'f' ]

  expect(a).toEqual(expectedResult)
  expect(b).toEqual(expectedResult)
})

test('with strings', () => {
  expect(concat('ABC', 'DEF')).toEqual('ABCDEF')
})

cond

cond(conditions: [Pred, (...a: readonly any[]) => any][]): (...a: readonly any[]) => any

It takes list with conditions and returns a new function fn that expects input as argument.

This function will start evaluating the conditions in order to find the first winner(order of conditions matter).

The winner is this condition, which left side returns true when input is its argument. Then the evaluation of the right side of the winner will be the final result.

If no winner is found, then fn returns undefined.

const fn = R.cond([
  [ x => x > 25, R.always('more than 25') ],
  [ x => x > 15, R.always('more than 15') ],
  [ R.T, x => `${x} is nothing special` ],
])

const result = [
  fn(30),
  fn(20),
  fn(10),
] 
// => ['more than 25', 'more than 15', '10 is nothing special']

Try the above R.cond example in Rambda REPL

All Typescript definitions
cond(conditions: [Pred, (...a: readonly any[]) => any][]): (...a: readonly any[]) => any;
cond<A, B>(conditions: [SafePred<A>, (...a: readonly A[]) => B][]): (...a: readonly A[]) => B;
Tests
import { always } from './always'
import { cond } from './cond'
import { equals } from './equals'
import { T } from './T'

test('returns a function', () => {
  expect(typeof cond([])).toEqual('function')
})

test('returns a conditional function', () => {
  const fn = cond([
    [ equals(0), always('water freezes at 0°C') ],
    [ equals(100), always('water boils at 100°C') ],
    [
      T,
      function (temp){
        return 'nothing special happens at ' + temp + '°C'
      },
    ],
  ])
  expect(fn(0)).toEqual('water freezes at 0°C')
  expect(fn(50)).toEqual('nothing special happens at 50°C')
  expect(fn(100)).toEqual('water boils at 100°C')
})

test('no winner', () => {
  const fn = cond([
    [ equals('foo'), always(1) ],
    [ equals('bar'), always(2) ],
  ])
  expect(fn('quux')).toEqual(undefined)
})

test('predicates are tested in order', () => {
  const fn = cond([
    [ T, always('foo') ],
    [ T, always('bar') ],
    [ T, always('baz') ],
  ])
  expect(fn()).toEqual('foo')
})

converge

converge(after: ((...a: readonly any[]) => any), fns: Array<((...a: readonly any[]) => any)>): (...a: readonly any[]) => any
All Typescript definitions
converge(after: ((...a: readonly any[]) => any), fns: Array<((...a: readonly any[]) => any)>): (...a: readonly any[]) => any;
Tests
import { add } from './add'
import { converge } from './converge'

const mult = (a, b) => a * b

const f1 = converge(mult, [ a => a + 1, a => a + 10 ])
const f2 = converge(mult, [ a => a + 1, (a, b) => a + b + 10 ])
const f3 = converge(mult, [ a => a + 1, (
  a, b, c
) => a + b + c + 10 ])

test('happy', () => {
  expect(f2(6, 7)).toEqual(161)
})

test('passes the results of applying the arguments individually', () => {
  const result = converge(mult)([ add(1), add(3) ])(2)
  expect(result).toEqual(15)
})

test('returns a function with the length of the longest argument', () => {
  expect(f1.length).toEqual(1)
  expect(f2.length).toEqual(2)
  expect(f3.length).toEqual(3)
})

test('passes context to its functions', () => {
  const a = function (x){
    return this.f1(x)
  }
  const b = function (x){
    return this.f2(x)
  }
  const c = function (x, y){
    return this.f3(x, y)
  }
  const d = converge(c, [ a, b ])
  const context = {
    f1 : add(1),
    f2 : add(2),
    f3 : add,
  }
  expect(a.call(context, 1)).toEqual(2)
  expect(b.call(context, 1)).toEqual(3)
  expect(d.call(context, 1)).toEqual(5)
})

test('works with empty functions list', () => {
  const fn = converge(function (){
    return arguments.length
  }, [])
  expect(fn.length).toEqual(0)
  expect(fn()).toEqual(0)
})

count

count<T>(searchFor: T, list: any[]): number

It counts how many times searchFor is within list according to R.equals.

const list = [1, {a:1}, 1, 'foo']
const searchFor = 1

const result = R.count(searchFor, list)
// => 2

Try the above R.count example in Rambda REPL

All Typescript definitions
count<T>(searchFor: T, list: any[]): number;
count<T>(searchFor: T): (list: any[]) => number;
Tests
import { count } from './count'

test('when 0', () => {
  const target = { a : 1 }
  const list = []

  const result = count(target, list)
  const expectedResult = 0

  expect(result).toEqual(expectedResult)
})

test('when 2', () => {
  const target = { a : 1 }
  const list = [ 2, 1, 2, { a : 1 }, 22, { a : 1 } ]

  const result = count(target)(list)
  const expectedResult = 2

  expect(result).toEqual(expectedResult)
})

curry

curry(fn: (...args: readonly any[]) => any): (...a: readonly any[]) => any

It expects a function as input and returns its curried version.

const fn = (a, b, c) => a + b + c
const curried = R.curry(fn)
const sum = curried(1,2)

const result = sum(3) // => 6

Try the above R.curry example in Rambda REPL

All Typescript definitions
curry(fn: (...args: readonly any[]) => any): (...a: readonly any[]) => any;
Tests
import { curry } from './curry'

test('happy', () => {
  const addFourNumbers = (
    a, b, c, d
  ) => a + b + c + d
  const curriedAddFourNumbers = curry(addFourNumbers)
  const f = curriedAddFourNumbers(1, 2)
  const g = f(3)

  expect(g(4)).toEqual(10)
})

test('when called with more arguments', () => {
  const add = curry((n, n2) => n + n2)

  expect(add(
    1, 2, 3
  )).toEqual(3)
})

test('when called with zero arguments', () => {
  const sub = curry((a, b) => a - b)
  const s0 = sub()

  expect(s0(5, 2)).toEqual(3)
})

test('when called via multiple curry stages', () => {
  const join = curry((
    a, b, c, d
  ) => [ a, b, c, d ].join('-'))

  const stage1 = join('A')
  const stage2 = stage1('B', 'C')

  expect(stage2('D')).toEqual('A-B-C-D')
})

curryN

curryN(length: number, fn: (...args: readonly any[]) => any): (...a: readonly any[]) => any

It returns a curried equivalent of the provided function, with the specified arity.

All Typescript definitions
curryN(length: number, fn: (...args: readonly any[]) => any): (...a: readonly any[]) => any;
Tests
import { curryN } from './curryN'

function source(
  a, b, c, d
){
  void d

  return a * b * c
}

test('accepts an arity', () => {
  const curried = curryN(3, source)
  expect(curried(1)(2)(3)).toEqual(6)
  expect(curried(1, 2)(3)).toEqual(6)
  expect(curried(1)(2, 3)).toEqual(6)
  expect(curried(
    1, 2, 3
  )).toEqual(6)
})

test('can be partially applied', () => {
  const curry3 = curryN(3)
  const curried = curry3(source)
  expect(curried.length).toEqual(3)
  expect(curried(1)(2)(3)).toEqual(6)
  expect(curried(1, 2)(3)).toEqual(6)
  expect(curried(1)(2, 3)).toEqual(6)
  expect(curried(
    1, 2, 3
  )).toEqual(6)
})

test('preserves context', () => {
  const ctx = { x : 10 }
  const f = function (a, b){
    return a + b * this.x
  }
  const g = curryN(2, f)

  expect(g.call(
    ctx, 2, 4
  )).toEqual(42)
  expect(g.call(ctx, 2).call(ctx, 4)).toEqual(42)
})

test('forwards extra arguments', () => {
  const f = function (){
    return Array.prototype.slice.call(arguments)
  }
  const g = curryN(3, f)

  expect(g(
    1, 2, 3
  )).toEqual([ 1, 2, 3 ])
  expect(g(
    1, 2, 3, 4
  )).toEqual([ 1, 2, 3, 4 ])
  expect(g(1, 2)(3, 4)).toEqual([ 1, 2, 3, 4 ])
  expect(g(1)(
    2, 3, 4
  )).toEqual([ 1, 2, 3, 4 ])
  expect(g(1)(2)(3, 4)).toEqual([ 1, 2, 3, 4 ])
})

debounce

debounce<T, U>(fn: (input: T) => U, ms: number): (input: T) => U

It creates a debounced function that delays invoking fn until after wait milliseconds ms have elapsed since the last time the debounced function was invoked.

let counter = 0
const increment = () => {
  counter++
}

const debounced = R.debounce(increment, 1000)

const result = async function(){
  debounced()
  await R.delay(500)
  debounced()
  await R.delay(800)
  console.log(counter) // => 0

  await R.delay(1200)
  console.log(counter) // => 1

  return counter
}
// `result` resolves to `1`

Try the above R.debounce example in Rambda REPL

All Typescript definitions
debounce<T, U>(fn: (input: T) => U, ms: number): (input: T) => U;
debounce<T, Q, U>(fn: (input1: T, input2: Q) => U, ms: number): (input1: T, input2: Q) => U;
debounce<T, Q, Z, U>(fn: (input1: T, input2: Q, input3: Z) => U, ms: number): (input1: T, input2: Q, input3: Z) => U;
Tests
import { debounce } from './debounce'
import { delay } from './delay'

test('happy', async () => {
  let counter = 0
  let aHolder
  let bHolder

  const inc = (a, b) => {
    aHolder = a
    bHolder = b
    counter++
  }
  const incWrapped = debounce(inc, 500)

  incWrapped(1, 2)
  expect(counter).toBe(0)
  expect(aHolder).toBe(undefined)
  expect(bHolder).toBe(undefined)

  await delay(200)

  incWrapped(2, 3)
  expect(counter).toBe(0)

  await delay(200)

  incWrapped(3, 4)
  expect(counter).toBe(0)
  expect(aHolder).toBe(undefined)
  expect(bHolder).toBe(undefined)

  await delay(200)
  incWrapped(5, 6)
  expect(counter).toBe(0)

  await delay(700)
  expect(counter).toBe(1)
  expect(aHolder).toBe(5)
  expect(bHolder).toBe(6)
})

test('immediate debounce', async () => {
  let counter = 0
  const inc = () => {
    counter++
  }

  const incWrapped = debounce(
    inc, 500, true
  )
  incWrapped()
  expect(counter).toBe(1)
  await delay(200)
  incWrapped()
  expect(counter).toBe(1)
  await delay(200)
  incWrapped()
  expect(counter).toBe(1)
  await delay(700)
  incWrapped()
  expect(counter).toBe(2)
})

dec

dec(x: number): number

It decrements a number.

All Typescript definitions
dec(x: number): number;
Tests
import { dec } from './dec'

test('happy', () => {
  expect(dec(2)).toBe(1)
})

defaultTo

defaultTo<T>(defaultValue: T): (...inputArguments: (T | null | undefined)[]) => T

It returns defaultValue, if all of inputArguments are undefined, null or NaN.

Else, it returns the first truthy inputArguments instance(from left to right).

// With single input argument
R.defaultTo('foo', 'bar') // => 'bar'
R.defaultTo('foo', undefined) // => 'foo'

// With multiple input arguments
R.defaultTo('foo', undefined, null, NaN) // => 'foo'
R.defaultTo('foo', undefined, 'bar', NaN, 'qux') // => 'bar'
R.defaultTo('foo', undefined, null, NaN, 'quz') // => 'qux'

Try the above R.defaultTo example in Rambda REPL

All Typescript definitions
defaultTo<T>(defaultValue: T): (...inputArguments: (T | null | undefined)[]) => T;
defaultTo<T>(defaultValue: T, ...inputArguments: (T | null | undefined)[]): T;
defaultTo<T, U>(defaultValue: T | U, ...inputArguments: (T | U | null | undefined)[]): T | U;
Tests
import { defaultTo } from './defaultTo'

test('with undefined', () => {
  expect(defaultTo('foo')(undefined)).toEqual('foo')
})

test('with null', () => {
  expect(defaultTo('foo')(null)).toEqual('foo')
})

test('with NaN', () => {
  expect(defaultTo('foo')(NaN)).toEqual('foo')
})

test('with empty string', () => {
  expect(defaultTo('foo', '')).toEqual('')
})

test('with false', () => {
  expect(defaultTo('foo', false)).toEqual(false)
})

test('when inputArgument passes initial check', () => {
  expect(defaultTo('foo', 'bar')).toEqual('bar')
})

test('default extends to indefinite input arguments - case 1', () => {
  const result = defaultTo(
    'foo', null, 'bar'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 2', () => {
  const result = defaultTo(
    'foo', null, NaN, 'bar'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 3', () => {
  const result = defaultTo(
    'foo', null, NaN, undefined
  )
  const expected = 'foo'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 4', () => {
  const result = defaultTo(
    'foo', null, NaN, undefined, 'bar'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 5', () => {
  const result = defaultTo(
    'foo', null, NaN, 'bar', 'baz'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 6', () => {
  const result = defaultTo(
    'foo', null, NaN, undefined, null, NaN
  )
  const expected = 'foo'

  expect(result).toEqual(expected)
})

delay

delay(ms: number): Promise<'RAMBDAX_DELAY'>

setTimeout as a promise that resolves to R.DELAY variable after ms milliseconds.

const result = R.delay(1000)
// `result` resolves to `RAMBDAX_DELAY`

Try the above R.delay example in Rambda REPL

All Typescript definitions
delay(ms: number): Promise<'RAMBDAX_DELAY'>;
Tests
import { DELAY, delay } from './delay'

test('usage with variables', async () => {
  expect(await delay(500)).toBe(DELAY)
})

difference

difference<T>(a: ReadonlyArray<T>, b: ReadonlyArray<T>): T[]

It returns the uniq set of all elements in the first list a not contained in the second list b.

const a = [ 1, 2, 3, 4 ]
const b = [ 3, 4, 5, 6 ]

const result = difference(a, b)
// => [ 1, 2 ]

Try the above R.difference example in Rambda REPL

All Typescript definitions
difference<T>(a: ReadonlyArray<T>, b: ReadonlyArray<T>): T[];
difference<T>(a: ReadonlyArray<T>): (b: ReadonlyArray<T>) => T[];
Tests
import { difference } from './difference'

test('difference', () => {
  const a = [ 1, 2, 3, 4 ]
  const b = [ 3, 4, 5, 6 ]
  expect(difference(a)(b)).toEqual([ 1, 2 ])

  expect(difference([], [])).toEqual([])
})

test('difference with objects', () => {
  const a = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const b = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(difference(a, b)).toEqual([ { id : 1 }, { id : 2 } ])
})

test('no duplicates in first list', () => {
  const M2 = [ 1, 2, 3, 4, 1, 2, 3, 4 ]
  const N2 = [ 3, 3, 4, 4, 5, 5, 6, 6 ]
  expect(difference(M2, N2)).toEqual([ 1, 2 ])
})

test('should use R.equals', () => {
  expect(difference([ NaN ], [ NaN ]).length).toEqual(0)
})

dissoc

dissoc<T>(prop: string, obj: any): T

It returns a new object that does not contain property prop.

R.dissoc('b', {a: 1, b: 2, c: 3})
//=> {a: 1, c: 3}

Try the above R.dissoc example in Rambda REPL

All Typescript definitions
dissoc<T>(prop: string, obj: any): T;
dissoc<T>(prop: string): (obj: any) => T;
Tests
import { dissoc } from './dissoc'

test('input is null or undefined', () => {
  expect(dissoc('b', null)).toEqual({})
  expect(dissoc('b', undefined)).toEqual({})
})

test('property exists curried', () => {
  expect(dissoc('b')({
    a : 1,
    b : 2,
  })).toEqual({ a : 1 })
})

test('property doesn\'t exists', () => {
  expect(dissoc('c', {
    a : 1,
    b : 2,
  })).toEqual({
    a : 1,
    b : 2,
  })
})

test('works with non-string property', () => {
  expect(dissoc(42, {
    a  : 1,
    42 : 2,
  })).toEqual({ a : 1 })

  expect(dissoc(null, {
    a    : 1,
    null : 2,
  })).toEqual({ a : 1 })

  expect(dissoc(undefined, {
    a         : 1,
    undefined : 2,
  })).toEqual({ a : 1 })
})

test('includes prototype properties', () => {
  function Rectangle(width, height){
    this.width = width
    this.height = height
  }
  const area = Rectangle.prototype.area = function (){
    return this.width * this.height
  }
  const rect = new Rectangle(7, 6)

  expect(dissoc('area', rect)).toEqual({
    width  : 7,
    height : 6,
  })

  expect(dissoc('width', rect)).toEqual({
    height : 6,
    area   : area,
  })

  expect(dissoc('depth', rect)).toEqual({
    width  : 7,
    height : 6,
    area   : area,
  })
})

divide

divide(x: number, y: number): number
R.divide(71, 100) // => 0.71

Try the above R.divide example in Rambda REPL

All Typescript definitions
divide(x: number, y: number): number;
divide(x: number): (y: number) => number;
Tests
import { divide } from './divide'

test('happy', () => {
  expect(divide(71, 100)).toEqual(0.71)
  expect(divide(71)(100)).toEqual(0.71)
})

drop

drop<T>(howMany: number, listOrString: ReadonlyArray<T>): T[]

It returns listOrString with howMany items dropped from its beginning.

R.drop(2, ['foo', 'bar', 'baz']) // => ['baz']
R.drop(2, 'foobar')  // => 'obar'

Try the above R.drop example in Rambda REPL

All Typescript definitions
drop<T>(howMany: number, listOrString: ReadonlyArray<T>): T[];
drop(howMany: number, listOrString: string): string;
drop<T>(howMany: number): {
  <T>(listOrString: readonly T[]): T[];
  (listOrString: string): string;
};
Tests
import assert from 'assert'

import { drop } from './drop'

test('with array', () => {
  expect(drop(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])
  expect(drop(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(drop(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(drop(3, 'rambda')).toEqual('bda')
})

test('with non-positive count', () => {
  expect(drop(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(drop(0, xs), xs)
  assert.notStrictEqual(drop(-1, xs), xs)
})

dropLast

dropLast<T>(howMany: number, listOrString: ReadonlyArray<T>): T[]

It returns listOrString with howMany items dropped from its end.

R.dropLast(2, ['foo', 'bar', 'baz']) // => ['foo']
R.dropLast(2, 'foobar')  // => 'foob'

Try the above R.dropLast example in Rambda REPL

All Typescript definitions
dropLast<T>(howMany: number, listOrString: ReadonlyArray<T>): T[];
dropLast(howMany: number, listOrString: string): string;
dropLast<T>(howMany: number): {
  <T>(listOrString: readonly T[]): T[];
  (listOrString: string): string;
};
Tests
import assert from 'assert'

import { dropLast } from './dropLast'

test('with array', () => {
  expect(dropLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo' ])
  expect(dropLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(dropLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(dropLast(3, 'rambda')).toEqual('ram')
})

test('with non-positive count', () => {
  expect(dropLast(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(dropLast(0, xs), xs)
  assert.notStrictEqual(dropLast(-1, xs), xs)
})

either

either(firstPredicate: Pred, secondPredicate: Pred): Pred

It returns a new predicate function from firstPredicate and secondPredicate inputs.

This predicate function will return true, if any of the two input predicates return true.

const firstPredicate = x => x > 10
const secondPredicate = x => x % 2 === 0
const predicate = R.either(firstPredicate, secondPredicate)

const result = [
  predicate(15),
  predicate(8),
  predicate(7),
]
//=> [true, true, false]

Try the above R.either example in Rambda REPL

All Typescript definitions
either(firstPredicate: Pred, secondPredicate: Pred): Pred;
either<T>(firstPredicate: Predicate<T>, secondPredicate: Predicate<T>): Predicate<T>;
either<T>(firstPredicate: Predicate<T>): (secondPredicate: Predicate<T>) => Predicate<T>;
either(firstPredicate: Pred): (secondPredicate: Pred) => Pred;
Tests
import { either } from './either'

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = either(between, total20)
  expect(fn(
    7, 8, 5
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return true
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  either(F, Z)()

  expect(effect).toBe('not evaluated')
})

test('case 1', () => {
  const firstFn = val => val > 0
  const secondFn = val => val * 5 > 10

  expect(either(firstFn, secondFn)(1)).toBeTrue()
})

test('case 2', () => {
  const firstFn = val => val > 0
  const secondFn = val => val === -10
  const fn = either(firstFn)(secondFn)

  expect(fn(-10)).toBeTrue()
})

endsWith

endsWith(target: string, str: string): boolean

Curried version of String.prototype.endsWith

const str = 'foo-bar'
const target = '-bar'

const result = R.endsWith(target, str)
// => true

Try the above R.endsWith example in Rambda REPL

All Typescript definitions
endsWith(target: string, str: string): boolean;
endsWith(target: string): (str: string) => boolean;
Tests
import { endsWith } from './endsWith'

test('happy', () => {
  expect(endsWith('bar', 'foo-bar')).toBeTrue()
  expect(endsWith('baz')('foo-bar')).toBeFalse()
})

test('does not work with arrays', () => {
  expect(() => endsWith([ 'c' ], [ 'a', 'b', 'c' ])).toThrowWithMessage(Error,
    'str.endsWith is not a function')
})

equals

equals<T>(x: T, y: T): boolean

It deeply compares x and y and returns true if they are equal.

R.equals(
  [1, {a:2}, [{b: 3}]],
  [1, {a:2}, [{b: 3}]]
) // => true

Try the above R.equals example in Rambda REPL

All Typescript definitions
equals<T>(x: T, y: T): boolean;
equals<T>(x: T): (y: T) => boolean;
Tests
import { equals } from './equals'

test('with array of objects', () => {
  const result = equals([ { a : 1 }, [ { b : 3 } ] ], [ { a : 2 }, [ { b : 3 } ] ])

  expect(result).toBeFalse()
})

test('with regex', () => {
  expect(equals(/s/, /s/)).toEqual(true)
  expect(equals(/s/, /d/)).toEqual(false)
  expect(equals(/a/gi, /a/gi)).toEqual(true)
  expect(equals(/a/gim, /a/gim)).toEqual(true)
  expect(equals(/a/gi, /a/i)).toEqual(false)
})

test('not a number', () => {
  expect(equals([ NaN ], [ NaN ])).toBeTrue()
})

test('new number', () => {
  expect(equals(new Number(0), new Number(0))).toEqual(true)
  expect(equals(new Number(0), new Number(1))).toEqual(false)
  expect(equals(new Number(1), new Number(0))).toEqual(false)
})

test('new string', () => {
  expect(equals(new String(''), new String(''))).toEqual(true)
  expect(equals(new String(''), new String('x'))).toEqual(false)
  expect(equals(new String('x'), new String(''))).toEqual(false)
  expect(equals(new String('foo'), new String('foo'))).toEqual(true)
  expect(equals(new String('foo'), new String('bar'))).toEqual(false)
  expect(equals(new String('bar'), new String('foo'))).toEqual(false)
})

test('new Boolean', () => {
  expect(equals(new Boolean(true), new Boolean(true))).toEqual(true)
  expect(equals(new Boolean(false), new Boolean(false))).toEqual(true)
  expect(equals(new Boolean(true), new Boolean(false))).toEqual(false)
  expect(equals(new Boolean(false), new Boolean(true))).toEqual(false)
})

test('new Error', () => {
  expect(equals(new Error('XXX'), {})).toEqual(false)
  expect(equals(new Error('XXX'), new TypeError('XXX'))).toEqual(false)
  expect(equals(new Error('XXX'), new Error('YYY'))).toEqual(false)
  expect(equals(new Error('XXX'), new Error('XXX'))).toEqual(true)
  expect(equals(new Error('XXX'), new TypeError('YYY'))).toEqual(false)
})

test('with dates', () => {
  expect(equals(new Date(0), new Date(0))).toEqual(true)
  expect(equals(new Date(1), new Date(1))).toEqual(true)
  expect(equals(new Date(0), new Date(1))).toEqual(false)
  expect(equals(new Date(1), new Date(0))).toEqual(false)
  expect(equals(new Date(0), {})).toEqual(false)
  expect(equals({}, new Date(0))).toEqual(false)
})

test('ramda spec', () => {
  expect(equals({}, {})).toEqual(true)

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toEqual(true)

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    b : 3,
    a : 2,
  })).toEqual(true)

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 3,
    b : 3,
  })).toEqual(false)

  expect(equals({
    a : 2,
    b : 3,
    c : 1,
  },
  {
    a : 2,
    b : 3,
  })).toEqual(false)
})

test('works with boolean tuple', () => {
  expect(equals([ true, false ], [ true, false ])).toBeTrue()
  expect(equals([ true, false ], [ true, true ])).toBeFalse()
})

test('works with equal objects within array', () => {
  const objFirst = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }
  const objSecond = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeTrue()
})

test('works with different objects within array', () => {
  const objFirst = { a : { b : 1 } }
  const objSecond = { a : { b : 2 } }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeFalse()
})

test('works with undefined as second argument', () => {
  expect(equals(1, undefined)).toBeFalse()

  expect(equals(undefined, undefined)).toBeTrue()
})

test('various examples', () => {
  expect(equals([ 1, 2, 3 ])([ 1, 2, 3 ])).toBeTrue()

  expect(equals([ 1, 2, 3 ], [ 1, 2 ])).toBeFalse()

  expect(equals(1, 1)).toBeTrue()

  expect(equals(1, '1')).toBeFalse()

  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    b : 2,
    a : 1,
  })).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : false,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    b : 2,
    a : 1,
    c : 3,
  })).toBeFalse()

  expect(equals({
    x : {
      a : 1,
      b : 2,
    },
  },
  {
    x : {
      b : 2,
      a : 1,
      c : 3,
    },
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    b : 3,
    a : 1,
  })).toBeFalse()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 1 } } })).toBeTrue()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 2 } } })).toBeFalse()

  expect(equals({ a : {} }, { a : {} })).toBeTrue()

  expect(equals('', '')).toBeTrue()

  expect(equals('foo', 'foo')).toBeTrue()

  expect(equals('foo', 'bar')).toBeFalse()

  expect(equals(0, false)).toBeFalse()

  expect(equals(/\s/g, null)).toBeFalse()

  expect(equals(null, null)).toBeTrue()

  expect(equals(false)(null)).toBeFalse()
})

test('with custom functions', () => {
  function foo(){
    return 1
  }
  foo.prototype.toString = () => ''
  const result = equals(foo, foo)

  expect(result).toBeFalse()
})

test('with classes', () => {
  class Foo{}
  const foo = new Foo()
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

F

F(): boolean
F() // => false

Try the above R.F example in Rambda REPL

All Typescript definitions
F(): boolean;

filter

filter<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[]

It filters list or object input with predicate.

const list = [3, 4, 3, 2]
const listPredicate = (x, index) => x - index > 2

const object = {abc: 'fo', xyz: 'bar', baz: 'foo'}
const objectPredicate = (x, prop) => x.length + prop.length > 5

const result = [
  R.filter(listPredicate, list),
  R.filter(objectPredicate, object)
]
// => [ [3, 4], { xyz: 'bar', baz: 'foo'} ]

Try the above R.filter example in Rambda REPL

All Typescript definitions
filter<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[];
filter<T>(predicate: FilterFunctionArray<T>, x: T[]): T[];
filter<T, U>(predicate: FilterFunctionObject<T>): (x: Dictionary<T>) => Dictionary<T>;
filter<T>(predicate: FilterFunctionObject<T>, x: Dictionary<T>): Dictionary<T>;
Tests
import Ramda from 'ramda'

import { F } from './F'
import { filter } from './filter'
import { T } from './T'

const sampleObject = {
  a : 1,
  b : 2,
  c : 3,
  d : 4,
}

test('happy', () => {
  const isEven = n => n % 2 === 0

  expect(filter(isEven, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
  expect(filter(isEven, {
    a : 1,
    b : 2,
    d : 3,
  })).toEqual({ b : 2 })
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(filter(T)(undefined)).toEqual([])
  expect(filter(F, null)).toEqual([])
  expect(() => Ramda.filter(T, null)).toThrowWithMessage(TypeError,
    'Cannot read property \'filter\' of null')
  expect(() => Ramda.filter(T, undefined)).toThrowWithMessage(TypeError,
    'Cannot read property \'filter\' of undefined')
})

test('predicate when input is object', () => {
  const obj = {
    a : 1,
    b : 2,
  }
  const predicate = (
    val, prop, inputObject
  ) => {
    expect(inputObject).toEqual(obj)
    expect(typeof prop).toEqual('string')

    return val < 2
  }
  expect(filter(predicate, obj)).toEqual({ a : 1 })
})

test('pass index as second argument', () => {
  let counter = 0
  filter((x, i) => {
    expect(i).toBe(counter)
    counter++
  },
  [ 10, 20, 30 ])
})

test('with object', () => {
  const isEven = n => n % 2 === 0
  const result = filter(isEven, sampleObject)
  const expectedResult = {
    b : 2,
    d : 4,
  }

  expect(result).toEqual(expectedResult)
})

filterAsync

filterAsync<T>(fn: AsyncPredicate<T>, list: T[]): Promise<T[]>

Asynchronous version of R.filter

const predicate = async x => {
  await R.delay(100)
  return x % 2 === 1
}
const result = await R.filterAsync(predicate, [ 1, 2, 3 ])
// => [ 1, 3 ]

Try the above R.filterAsync example in Rambda REPL

All Typescript definitions
filterAsync<T>(fn: AsyncPredicate<T>, list: T[]): Promise<T[]>;
filterAsync<T>(fn: AsyncPredicateIndexed<T>, list: T[]): Promise<T[]>;
filterAsync<T>(fn: AsyncPredicate<T>) : ( list: T[]) => Promise<T[]>;
filterAsync<T>(fn: AsyncPredicateIndexed<T>) : ( list: T[]) => Promise<T[]>;
Tests
import { delay } from './delay'
import { filterAsync } from './filterAsync'

test('happy', async () => {
  const predicate = async x => {
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate)([ 1, 2, 3 ])
  expect(result).toEqual([ 1, 3 ])
})

test('with object', async () => {
  const predicate = async (x, prop) => {
    expect(typeof prop).toBe('string')
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate, {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
    e : 5,
  })

  expect(result).toEqual({
    a : 1,
    c : 3,
    e : 5,
  })
})

find

find<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): T | undefined

It returns the first element of list that satisfy the predicate.

If there is no such element, it returns undefined.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.find(predicate, list)
// => {foo: 1}

Try the above R.find example in Rambda REPL

All Typescript definitions
find<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): T | undefined;
find<T>(predicate: (x: T, index: number) => boolean, list: ReadonlyArray<T>): T | undefined;
find<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => T | undefined;
find<T>(predicate: (x: T, index: number) => boolean): (list: ReadonlyArray<T>) => T | undefined;
Tests
import { find } from './find'
import { propEq } from './propEq'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  const fn = propEq('a', 2)
  expect(find(fn, list)).toEqual({ a : 2 })
})

test('with curry', () => {
  const fn = propEq('a', 4)
  expect(find(fn)(list)).toBeUndefined()
})

test('with empty list', () => {
  expect(find(() => true, [])).toBeUndefined()
})

test('pass index', () => {
  find((_, i) => {
    expect(i).toBe(0)
  },
  [ 'foo' ])
})

findIndex

findIndex<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): number

It returns the index of the first element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.findIndex(predicate, list)
// => 1

Try the above R.findIndex example in Rambda REPL

All Typescript definitions
findIndex<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): number;
findIndex<T>(predicate: (x: T, index: number) => boolean, list: ReadonlyArray<T>): number;
findIndex<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => number;
findIndex<T>(predicate: (x: T, index: number) => boolean): (list: ReadonlyArray<T>) => number;
Tests
import { findIndex } from './findIndex'
import { propEq } from './propEq'

test('happy', () => {
  expect(findIndex(propEq('a', 2))([ { a : 1 }, { a : 2 }, { a : 3 } ])).toEqual(1)

  expect(findIndex(propEq('a', 1))([ { a : 1 }, { a : 2 }, { a : 3 } ])).toEqual(0)

  expect(findIndex(propEq('a', 4))([ { a : 1 }, { a : 2 }, { a : 3 } ])).toEqual(-1)
})

test('pass index as second argument', () => {
  findIndex((x, i) => {
    expect(typeof x).toBe('number')
    expect(typeof i).toBe('number')
  })([ 10, 12, 15 ])
})

findLast

findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined

It returns the last element of list satisfying the predicate function.

If there is no such element, then undefined is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLast(predicate, list)
// => {foo: 1}

Try the above R.findLast example in Rambda REPL

All Typescript definitions
findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined;
findLast<T>(fn: (x: T, index: number) => boolean, list: T[]): T | undefined;
findLast<T>(fn: (x: T) => boolean): (list: T[]) => T | undefined;
findLast<T>(fn: (x: T, index: number) => boolean): (list: T[]) => T | undefined;
Tests
import { findLast } from './findLast'

test('happy', () => {
  const result = findLast((x, i) => {
    expect(typeof i).toBe('number')

    return x > 1
  },
  [ 1, 1, 1, 2, 3, 4, 1 ])
  expect(result).toEqual(4)

  expect(findLast(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toEqual(0)
})

test('with curry', () => {
  expect(findLast(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toEqual(4)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLast(even, a)).toEqual(0)
  expect(findLast(gt100, a)).toEqual(300)
  expect(findLast(isStr, a)).toEqual('cow')
  expect(findLast(xGt100, a)).toEqual(obj2)
})

test('ramda 2', () => {
  expect(findLast(even, [ 'zing' ])).toEqual(undefined)
})

test('ramda 3', () => {
  expect(findLast(even, [ 2, 3, 5 ])).toEqual(2)
})

test('ramda 4', () => {
  expect(findLast(even, [])).toEqual(undefined)
})

findLastIndex

findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the last element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLastIndex(predicate, list)
// => 1

Try the above R.findLastIndex example in Rambda REPL

All Typescript definitions
findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number;
findLastIndex<T>(predicate: (x: T, index: number) => boolean, list: T[]): number;
findLastIndex<T>(predicate: (x: T) => boolean): (list: T[]) => number;
findLastIndex<T>(predicate: (x: T, index: number) => boolean): (list: T[]) => number;
Tests
import { findLastIndex } from './findLastIndex'

test('happy', () => {
  const result = findLastIndex((x, i) => {
    expect(typeof i).toBe('number')

    return x > 1
  },
  [ 1, 1, 1, 2, 3, 4, 1 ])

  expect(result).toEqual(5)

  expect(findLastIndex(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toEqual(0)
})

test('with curry', () => {
  expect(findLastIndex(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toEqual(5)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLastIndex(even, a)).toEqual(15)
  expect(findLastIndex(gt100, a)).toEqual(9)
  expect(findLastIndex(isStr, a)).toEqual(3)
  expect(findLastIndex(xGt100, a)).toEqual(10)
})

test('ramda 2', () => {
  expect(findLastIndex(even, [ 'zing' ])).toEqual(-1)
})

test('ramda 3', () => {
  expect(findLastIndex(even, [ 2, 3, 5 ])).toEqual(0)
})

test('ramda 4', () => {
  expect(findLastIndex(even, [])).toEqual(-1)
})

flatten

flatten<T>(list: ReadonlyArray<any>): T[]

It deeply flattens an array.

const result = R.flatten([
  1, 
  2, 
  [3, 30, [300]], 
  [4]
])
// => [ 1, 2, 3, 30, 300, 4 ]

Try the above R.flatten example in Rambda REPL

All Typescript definitions
flatten<T>(list: ReadonlyArray<any>): T[];
Tests
import { flatten } from './flatten'

test('happy', () => {
  expect(flatten([ 1, 2, 3, [ [ [ [ [ 4 ] ] ] ] ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ 3 ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ [ 3 ] ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, 2, [ 3, 4 ], 5, [ 6, [ 7, 8, [ 9, [ 10, 11 ], 12 ] ] ] ])).toEqual([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ])
})

test('readme example', () => {
  const result = flatten([ 1, 2, [ 3, 30, [ 300 ] ], [ 4 ] ])
  expect(result).toEqual([ 1, 2, 3, 30, 300, 4 ])
})

flip

flip<T, U, TResult>(fn: (arg0: T, arg1: U) => TResult): (arg1: U, arg0?: T) => TResult

It returns function which calls fn with exchanged first and second argument.

const subtractFlip = R.flip(R.subtract)

const result = [
  subtractFlip(1,7),
  R.flip(1, 6)
]  
// => [6, -6]

Try the above R.flip example in Rambda REPL

All Typescript definitions
flip<T, U, TResult>(fn: (arg0: T, arg1: U) => TResult): (arg1: U, arg0?: T) => TResult;
flip<F extends (...args: any) => any, P extends FunctionToolbelt.Parameters<F>>(fn: F): FunctionToolbelt.Curry<(...args: ListToolbelt.Merge<[P[1], P[0]], P>) => FunctionToolbelt.Return<F>>;
Tests
import { flip } from './flip'
import { subtract } from './subtract'
import { update } from './update'

test('function with arity of 2', () => {
  const subtractFlipped = flip(subtract)

  expect(subtractFlipped(1)(7)).toEqual(6)
  expect(subtractFlipped(1, 7)).toEqual(6)
  expect(subtractFlipped(
    1, 7, 9
  )).toEqual(6)
})

test('function with arity of 3', () => {
  const updateFlipped = flip(update)

  const result = updateFlipped(
    88, 0, [ 1, 2, 3 ]
  )
  const curriedResult = updateFlipped(88, 0)([ 1, 2, 3 ])
  const tripleCurriedResult = updateFlipped(88)(0)([ 1, 2, 3 ])
  expect(result).toEqual([ 88, 2, 3 ])
  expect(curriedResult).toEqual([ 88, 2, 3 ])
  expect(tripleCurriedResult).toEqual([ 88, 2, 3 ])
})

test('function with arity of 4', () => {
  const testFunction = (
    a, b, c, d
  ) => `${ a - b }==${ c - d }`
  const testFunctionFlipped = flip(testFunction)

  const result = testFunction(
    1, 2, 3, 4
  )
  const flippedResult = testFunctionFlipped(
    2, 1, 3, 4
  )
  expect(result).toEqual(flippedResult)
  expect(result).toEqual('-1==-1')
})

test('function with arity of 5', () => {
  const testFunction = (
    a, b, c, d, e
  ) => `${ a - b }==${ c - d - e }`
  const testFunctionFlipped = flip(testFunction)

  expect(() => testFunctionFlipped(
    1, 2, 3, 4, 5
  )).toThrowWithMessage(Error,
    'R.flip doesn\'t work with arity > 4')
})

forEach

forEach<T, U>(fn: MapFunctionObject<T, U>, list: Dictionary<T>): Dictionary<T>

It applies iterable function over all members of list and returns list.

const sideEffect = {}
const result = R.forEach(
  x => sideEffect[`foo${x}`] = x
)([1, 2])

sideEffect //=> {foo1: 1, foo2: 2}
result //=> [1, 2]

Try the above R.forEach example in Rambda REPL

All Typescript definitions
forEach<T, U>(fn: MapFunctionObject<T, U>, list: Dictionary<T>): Dictionary<T>;
forEach<T, U>(fn: MapFunctionArray<T, U>, list: T[]): T[];
forEach<T, U>(fn: MapFunctionArray<T, U>): (list: T[]) => T[];
forEach<T, U, S>(fn: MapFunctionObject<T, U>): (list: Dictionary<T>) => Dictionary<T>;
forEach<T>(fn: MapFunctionArray<T, T>): (list: T[]) => T[];
forEach<T>(fn: MapFunctionArray<T, T>, list: ReadonlyArray<T>): T[];
Tests
import { forEach } from './forEach'
import { type } from './type'

test('iterate over object', () => {
  const obj = {
    a : 1,
    b : [ 1, 2 ],
    c : { d : 7 },
    f : 'foo',
  }
  const result = {}
  const returned = forEach((
    val, prop, inputObj
  ) => {
    expect(type(inputObj)).toBe('Object')
    result[ prop ] = `${ prop }-${ type(val) }`
  })(obj)

  const expected = {
    a : 'a-Number',
    b : 'b-Array',
    c : 'c-Object',
    f : 'f-String',
  }

  expect(result).toEqual(expected)
  expect(returned).toEqual(obj)
})

test('happy', () => {
  const sideEffect = {}
  forEach(x => sideEffect[ `foo${ x }` ] = x + 10)([ 1, 2 ])

  expect(sideEffect).toEqual({
    foo1 : 11,
    foo2 : 12,
  })
})

test('happy 2', () => {
  const list = [
    {
      x : 1,
      y : 2,
    },
    {
      x : 100,
      y : 200,
    },
    {
      x : 300,
      y : 400,
    },
    {
      x : 234,
      y : 345,
    },
  ]
  const sideEffect = {}
  const result = forEach(elem => {
    sideEffect[ elem.x ] = elem.y
  }, list)
  const expectedSideEffect = {
    1   : 2,
    100 : 200,
    300 : 400,
    234 : 345,
  }

  expect(sideEffect).toEqual(expectedSideEffect)
  expect(result).toEqual(list)
})

test('with empty list', () => {
  const list = []
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('with wrong input', () => {
  const list = undefined
  const result = forEach(x => x * x)(list)

  expect(result).toBeUndefined()
})

test('returns the input', () => {
  const list = [ 1, 2, 3 ]
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('pass index as second argument', () => {
  const list = [ 11, 21, 31 ]
  const indexes = []
  const result = forEach((x, i) => indexes.push(i))(list)

  expect(indexes).toEqual([ 0, 1, 2 ])
})

fromPairs

fromPairs<V>(listOfPairs: KeyValuePair<string, V>[]): { [index: string]: V }

It transforms a listOfPairs to an object.

const listOfPairs = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]
const expected = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}

const result = R.fromPairs(listOfPairs)
// => `result` is equal to `expected`

Try the above R.fromPairs example in Rambda REPL

All Typescript definitions
fromPairs<V>(listOfPairs: KeyValuePair<string, V>[]): { [index: string]: V };
fromPairs<V>(listOfPairs: KeyValuePair<number, V>[]): { [index: number]: V };
Tests
import { fromPairs } from './fromPairs'

const list = [
  [ 'a', 1 ],
  [ 'b', 2 ],
  [ 'c', [ 3, 4 ] ],
]
const expected = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}

test('happy', () => {
  expect(fromPairs(list)).toEqual(expected)
})

getter

getter<T>(keyOrKeys: string | string[] | undefined): T

The set of methods R.setter, R.getter and R.reset allow different parts of your logic to access comminicate indirectly via shared cache object.

Usually these methods show that you might need to refactor to classes. Still, they can be helpful meanwhile.

R.getter: It provides access to the cache object. If undefined is used as a key, this method will return the whole cache object. If string is passed, then it will return cache value for this key. If array of string is passed, then it assume that this is array of keys and it will return the corresponding cache values for these keys.

R.setter: It allows cache object's keys to be changed. You can either set individual key-value pairs with R.setter(key, value) or you pass directly object, which will be merged with the cache object.

R.reset: It resets the cache object.

R.setter('foo','bar')
R.setter('a', 1)
R.getter(['foo','a']) // => {foo: 'bar', a: 1}

R.setter('a', 2)
R.getter('a') // => 2
R.reset()
R.getter('a') // => undefined

Try the above R.getter example in Rambda REPL

All Typescript definitions
getter<T>(keyOrKeys: string | string[] | undefined): T;
Tests
import { add } from './add'
import { getter, reset, setter } from './getter'

afterEach(() => {
  reset()
})

test('happy', () => {
  const key = 'foo'
  setter(key, 1)

  expect(getter(key)).toBe(1)
})

test('docs example', () => {
  setter('foo', 'bar')
  setter('a', 1)
  expect(getter([ 'foo', 'a' ])).toEqual({
    foo : 'bar',
    a   : 1,
  })

  setter('a', 2)
  expect(getter('a')).toBe(2)
  reset()
  expect(getter('a')).toBeUndefined()
})

test('when array is key in getter', () => {
  setter({
    a : 1,
    b : 2,
    c : 3,
  })

  expect(getter([ 'a', 'b' ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('getter with undefined as key returns all', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)

  expect(getter()).toEqual(data)
})

test('function as setter value', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)
  setter('a', add(10))

  expect(getter()).toEqual({
    a : 11,
    b : 2,
    c : 3,
  })
})

test('setter fallbacks to undefined', () => {
  expect(setter()).toBeUndefined
})

glue

glue(input: string, glueString?: string): string

It transforms multiline string to single line by gluing together the separate lines with the glueString and removing the empty spaces. By default glueString is equal to single space, so if that is what you need, then you can just pass a single argument.

const result = R.glue(`
  foo
  bar
  baz
`)
// => 'foo bar baz'

Try the above R.glue example in Rambda REPL

All Typescript definitions
glue(input: string, glueString?: string): string;
Tests
import { glue } from './glue'

test('empty string as a glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '')

  const expectedResult = 'foobarbaz'

  expect(result).toBe(expectedResult)
})

test('case 0', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = false
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 1', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = true
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } --env=node ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 2', () => {
  const first = '--runInBand'
  const result = glue(`
    zero
    ${ first }
    last
  `)
  const expectedResult = `zero ${ first } last`

  expect(result).toBe(expectedResult)
})

test('case 3', () => {
  const result = glue(`
    foo
    bar
    baz
  `)

  const expectedResult = 'foo bar baz'

  expect(result).toBe(expectedResult)
})

test('with glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '==')

  const expectedResult = 'foo==bar==baz'

  expect(result).toBe(expectedResult)
})

groupBy

groupBy<T>(groupFn: (x: T) => string, list: ReadonlyArray<T>): { [index: string]: T[] }

It splits list according to a provided groupFn function and returns an object.

const list = [ 'a', 'b', 'aa', 'bb' ]
const groupFn = x => x.length

const result = R.groupBy(groupFn, list)
// => { '1': ['a', 'b'], '2': ['aa', 'bb'] }

Try the above R.groupBy example in Rambda REPL

All Typescript definitions
groupBy<T>(groupFn: (x: T) => string, list: ReadonlyArray<T>): { [index: string]: T[] };
groupBy<T>(groupFn: (x: T) => string): (list: ReadonlyArray<T>) => { [index: string]: T[] };
Tests
import { groupBy } from './groupBy'
import { prop } from './prop'

test('groupBy', () => {
  const list = [
    {
      age  : 12,
      name : 'john',
    },
    {
      age  : 12,
      name : 'jack',
    },
    {
      age  : 24,
      name : 'mary',
    },
    {
      age  : 24,
      name : 'steve',
    },
  ]
  const expectedResult = {
    12 : [
      {
        age  : 12,
        name : 'john',
      },
      {
        age  : 12,
        name : 'jack',
      },
    ],
    24 : [
      {
        age  : 24,
        name : 'mary',
      },
      {
        age  : 24,
        name : 'steve',
      },
    ],
  }

  expect(groupBy(prop('age'))(list)).toEqual(expectedResult)
  expect(groupBy(prop('age'), list)).toEqual(expectedResult)
})

groupWith

groupWith<T>(compareFn: (x: T, y: T) => boolean): (list: ReadonlyArray<T>) => T[][]

It returns separated version of list, where separation is done with equality compareFn function.

const compareFn = (x, y) => x === y
const list = [1, 2, 2, 1, 1, 2]

const result = R.groupWith(isConsecutive, list)
// => [[1], [2,2], [1,1], [2]]

Try the above R.groupWith example in Rambda REPL

All Typescript definitions
groupWith<T>(compareFn: (x: T, y: T) => boolean): (list: ReadonlyArray<T>) => T[][];
groupWith<T>(compareFn: (x: T, y: T) => boolean, list: ReadonlyArray<T>): T[][];
groupWith<T>(compareFn: (x: T, y: T) => boolean, list: string): string[];
Tests
import { equals } from './equals'
import { groupWith } from './groupWith'

test('issue is fixed', () => {
  const result = groupWith(equals, [ 1, 2, 2, 3 ])
  const expected = [ [ 1 ], [ 2, 2 ], [ 3 ] ]
  expect(result).toEqual(expected)
})

test('long list', () => {
  const result = groupWith(equals, [
    0,
    1,
    1,
    2,
    3,
    5,
    8,
    13,
    21,
    21,
    21,
    1,
    2,
  ])

  const expected = [
    [ 0 ],
    [ 1, 1 ],
    [ 2 ],
    [ 3 ],
    [ 5 ],
    [ 8 ],
    [ 13 ],
    [ 21, 21, 21 ],
    [ 1 ],
    [ 2 ],
  ]
  expect(result).toEqual(expected)
})

test('readme example', () => {
  const list = [ 4, 3, 6, 2, 2, 1 ]

  const result = groupWith((a, b) => a - b === 1, list)
  const expected = [ [ 4, 3 ], [ 6 ], [ 2 ], [ 2, 1 ] ]
  expect(result).toEqual(expected)
})

test('throw with string as input', () => {
  expect(() => groupWith(equals, 'Mississippi')).toThrowWithMessage(TypeError,
    'list.reduce is not a function')
})

const isConsecutive = function (a, b){
  return a + 1 === b
}

test('fix coverage', () => {
  expect(groupWith(isConsecutive, [ 1, 2, 3, 0 ])).toEqual([ [ 1, 2, 3 ], [ 0 ] ])
})

test('from ramda 0', () => {
  expect(groupWith(equals, [])).toEqual([])
  expect(groupWith(isConsecutive, [])).toEqual([])
})

test('from ramda 1', () => {
  expect(groupWith(isConsecutive, [ 4, 3, 2, 1 ])).toEqual([
    [ 4 ],
    [ 3 ],
    [ 2 ],
    [ 1 ],
  ])
})

test('from ramda 2', () => {
  expect(groupWith(isConsecutive, [ 1, 2, 3, 4 ])).toEqual([ [ 1, 2, 3, 4 ] ])
})

test('from ramda 3', () => {
  expect(groupWith(isConsecutive, [ 1, 2, 2, 3 ])).toEqual([
    [ 1, 2 ],
    [ 2, 3 ],
  ])
  expect(groupWith(isConsecutive, [ 1, 2, 9, 3, 4 ])).toEqual([
    [ 1, 2 ],
    [ 9 ],
    [ 3, 4 ],
  ])
})

test('list with single item', () => {
  const result = groupWith(equals, [ 0 ])

  const expected = [ [ 0 ] ]
  expect(result).toEqual(expected)
})

has

has<T>(prop: string, obj: T): boolean

It returns true if obj has property prop.

const obj = {a: 1}

const result = [
  R.has('a', obj),
  R.has('b', obj)
]
// => [true, false]

Try the above R.has example in Rambda REPL

All Typescript definitions
has<T>(prop: string, obj: T): boolean;
has(prop: string): <T>(obj: T) => boolean;
Tests
import { has } from './has'

test('happy', () => {
  expect(has('a')({ a : 1 })).toBeTrue()
  expect(has('b', { a : 1 })).toBeFalse()
})

test('with non-object', () => {
  expect(has('a', undefined)).toEqual(false)
  expect(has('a', null)).toEqual(false)
  expect(has('a', true)).toEqual(false)
  expect(has('a', '')).toEqual(false)
  expect(has('a', /a/)).toEqual(false)
})

hasPath

hasPath<T>(
  path: string | string[],
  input: object
): boolean

It will return true, if input object has truthy path(calculated with R.path).

const path = 'a.b'
const pathAsArray = ['a', 'b']
const obj = {a: {b: []}}

const result = [
  R.hasPath(path, obj),
  R.hasPath(pathAsArray, obj),
  R.hasPath('a.c', obj),
]
// => [true, true, false]

Try the above R.hasPath example in Rambda REPL

All Typescript definitions
hasPath<T>(
  path: string | string[],
  input: object
): boolean;
hasPath<T>(
  path: string | string[]
): (input: object) => boolean;
Tests
import { hasPath } from './hasPath'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : [] } }

  const result = hasPath(path)(obj)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const path = 'a.b'
  const obj = {}

  const result = hasPath(path, obj)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})
head<T>(listOrString: T[]): T | undefined

It returns the first element of listOrString.

const result = [
  R.head([1, 2, 3]),
  R.head('foo') 
]
// => [1, 'f']

Try the above R.head example in Rambda REPL

All Typescript definitions
head<T>(listOrString: T[]): T | undefined;
head(listOrString: string): string;
Tests
import { head } from './head'

test('head', () => {
  expect(head([ 'fi', 'fo', 'fum' ])).toEqual('fi')
  expect(head([])).toEqual(undefined)
  expect(head('foo')).toEqual('f')
  expect(head('')).toEqual('')
})

identical

identical<T>(x: T, y: T): boolean

It returns true if its arguments a and b are identical.

Otherwise, it returns false.

const obj = {a: 1};
R.identical(obj, obj); //=> true
R.identical(1, 1); //=> true
R.identical(1, '1'); //=> false
R.identical([], []); //=> false
R.identical(0, -0); //=> false
R.identical(NaN, NaN); //=> true

Try the above R.identical example in Rambda REPL

All Typescript definitions
identical<T>(x: T, y: T): boolean;
identical<T>(x: T): (y: T) => boolean;
Tests
import { F, T } from '../rambda'
import { _isInteger } from './_internals/_isInteger'
import { _objectIs } from './_internals/_objectIs'
import { identical } from './identical'

test('with boolean', () => {
  expect(F()).toBeFalse()
  expect(T()).toBeTrue()
})

test('internal isInteger', () => {
  expect(_isInteger(1)).toBeTrue()
  expect(_isInteger(0.3)).toBeFalse()
})

test('internal objectIs', () => {
  expect(_objectIs(1, 1)).toBeTrue()
  expect(_objectIs(NaN, NaN)).toBeTrue()
})

test('identical', () => {
  const a = {}

  expect(identical(100)(100)).toEqual(true)
  expect(identical(100, '100')).toEqual(false)
  expect(identical('string', 'string')).toEqual(true)
  expect(identical([], [])).toEqual(false)
  expect(identical(a, a)).toEqual(true)
  expect(identical(undefined, undefined)).toEqual(true)
  expect(identical(null, undefined)).toEqual(false)
})

identity

identity<T>(input: T): T

It just passes back the supplied input argument.

R.identity(7) // => 7

Try the above R.identity example in Rambda REPL

All Typescript definitions
identity<T>(input: T): T;
Tests
import { identity } from './identity'

test('happy', () => {
  expect(identity(7)).toEqual(7)
  expect(identity(true)).toEqual(true)
  expect(identity({ a : 1 })).toEqual({ a : 1 })
})

ifElse

ifElse<T, U>(
  condition: (x: T) => boolean, 
  onTrue: (x: T) => U, 
  onFalse: (x: T) => U, 
): (x: T) => U

It expects condition, onTrue and onFalse functions as inputs and it returns a new function with example name of fn.

When fn`` is called with inputargument, it will return eitheronTrue(input)oronFalse(input)depending oncondition(input)` evaluation.

const fn = R.ifElse(
 x => x>10,
 x => x*2,
 x => x*10
)

const result = [ fn(8), fn(18) ]
// => [80, 36]

Try the above R.ifElse example in Rambda REPL

All Typescript definitions
ifElse<T, U>(
  condition: (x: T) => boolean, 
  onTrue: (x: T) => U, 
  onFalse: (x: T) => U, 
): (x: T) => U;
ifElse<T, K, U>(
  condition: (x: T, y: K) => boolean, 
  onTrue: (x: T, y: K) => U, 
  onFalse: (x: T, y: K) => U, 
): (x: T, y: K) => U;
Tests
import { always } from './always'
import { has } from './has'
import { identity } from './identity'
import { ifElse } from './ifElse'
import { prop } from './prop'

const condition = has('foo')
const v = function (a){
  return typeof a === 'number'
}
const t = function (a){
  return a + 1
}
const ifFn = x => prop('foo', x).length
const elseFn = () => false

test('happy', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toEqual(3)
  expect(fn({ fo : 'bar' })).toEqual(false)
})

test('ramda spec', () => {
  const ifIsNumber = ifElse(v)
  expect(ifIsNumber(t, identity)(15)).toEqual(16)
  expect(ifIsNumber(t, identity)('hello')).toEqual('hello')
})

test('pass all arguments', () => {
  const identity = function (a){
    return a
  }
  const v = function (){
    return true
  }
  const onTrue = function (a, b){
    expect(a).toEqual(123)
    expect(b).toEqual('abc')
  }
  ifElse(
    v, onTrue, identity
  )(123, 'abc')
})

test('accept constant as condition', () => {
  const fn = ifElse(true)(always(true))(always(false))

  expect(fn()).toEqual(true)
})

test('accept constant as condition - case 2', () => {
  const fn = ifElse(
    false, always(true), always(false)
  )

  expect(fn()).toEqual(false)
})

test('curry 1', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toEqual(3)
  expect(fn({ fo : 'bar' })).toEqual(false)
})

test('curry 2', () => {
  const fn = ifElse(condition)(ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toEqual(3)
  expect(fn({ fo : 'bar' })).toEqual(false)
})

test('simple arity of 1', () => {
  const condition = x => x > 5
  const onTrue = x => x + 1
  const onFalse = x => x + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1)
  expect(result).toBe(11)
})

test('simple arity of 2', () => {
  const condition = (x, y) => x + y > 5
  const onTrue = (x, y) => x + y + 1
  const onFalse = (x, y) => x + y + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1, 10)
  expect(result).toBe(12)
})

ifElseAsync

ifElseAsync<T, U>(
  condition: (x: T) => Promise<boolean>, 
  onTrue: (x: T) => U, 
  onFalse: (x: T) => U, 
  ): (x: T) => Promise<U>

Asynchronous version of R.ifElse. Any of condition, ifFn and elseFn can be either asynchronous or synchronous function.

const condition = async x => {
  await R.delay(100)
  return x > 1
}
const ifFn = async x => {
  await R.delay(100)
  return x + 1
}
const elseFn = async x => {
  await R.delay(100)
  return x - 1
}

const result = await R.ifElseAsync(
  condition,
  ifFn,
  elseFn  
)(1)
// => 0

Try the above R.ifElseAsync example in Rambda REPL

All Typescript definitions
ifElseAsync<T, U>(
  condition: (x: T) => Promise<boolean>, 
  onTrue: (x: T) => U, 
  onFalse: (x: T) => U, 
  ): (x: T) => Promise<U>;
ifElseAsync<T, U>(
  condition: (x: T) => boolean, 
  onTrue: (x: T) => Promise<U>, 
  onFalse: (x: T) => Promise<U>, 
): (x: T) => Promise<U>;
ifElseAsync<T, U>(
  condition: (x: T) => Promise<boolean>, 
  onTrue: (x: T) => Promise<U>, 
  onFalse: (x: T) => Promise<U>, 
): (x: T) => Promise<U>;
ifElseAsync<T, K, U>(
  condition: (x: T, y: K) => Promise<boolean>, 
  onTrue: (x: T, y: K) => U, 
  onFalse: (x: T, y: K) => U, 
): (x: T, y: K) => Promise<U>;
ifElseAsync<T, K, U>(
  condition: (x: T, y: K) => boolean, 
  onTrue: (x: T, y: K) => Promise<U>, 
  onFalse: (x: T, y: K) => Promise<U>, 
): (x: T, y: K) => Promise<U>;
ifElseAsync<T, K, U>(
  condition: (x: T, y: K) => Promise<boolean>, 
  onTrue: (x: T, y: K) => Promise<U>, 
  onFalse: (x: T, y: K) => Promise<U>, 
): (x: T, y: K) => Promise<U>;
Tests
import { delay } from './delay'
import { ifElseAsync } from './ifElseAsync'

test('arity of 1 - condition is async', async () => {
  const condition = async x => {
    await delay(100)

    return x > 4
  }
  const whenTrue = x => x + 1
  const whenFalse = x => x + 10
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 1 - condition is sync', async () => {
  const condition = x => x > 4
  const whenTrue = async x => {
    await delay(100)

    return x + 1
  }
  const whenFalse = async x => {
    await delay(100)

    return x + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 1 - all inputs are async', async () => {
  const condition = async x => {
    await delay(100)

    return x > 4
  }
  const whenTrue = async x => {
    await delay(100)

    return x + 1
  }
  const whenFalse = async x => {
    await delay(100)

    return x + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 2 - condition is async', async () => {
  const condition = async (x, y) => {
    await delay(100)

    return x + y > 4
  }
  const whenTrue = (x, y) => x + y + 1
  const whenFalse = (x, y) => x + y + 10
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

test('arity of 2 - condition is sync', async () => {
  const condition = (x, y) => x + y > 4
  const whenTrue = async (x, y) => {
    await delay(100)

    return x + y + 1
  }
  const whenFalse = async (x, y) => {
    await delay(100)

    return x + y + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

test('arity of 2 - all inputs are async', async () => {
  const condition = async (x, y) => {
    await delay(100)

    return x + y > 4
  }
  const whenTrue = async (x, y) => {
    await delay(100)

    return x + y + 1
  }
  const whenFalse = async (x, y) => {
    await delay(100)

    return x + y + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

inc

inc(x: number): number

It increments a number.

R.inc(1) // => 2

Try the above R.inc example in Rambda REPL

All Typescript definitions
inc(x: number): number;
Tests
import { inc } from './inc'

test('happy', () => {
  expect(inc(1)).toBe(2)
})

includes

includes(valueToFind: string, input: ReadonlyArray<string> | string): boolean

If input is string, then this method work as native String.includes.

If input is array, then R.equals is used to define if valueToFind belongs to the list.

const result = [
  R.includes('oo', 'foo'),
  R.includes({a: 1}, [{a: 1}])
]
// => [true, true ]

Try the above R.includes example in Rambda REPL

All Typescript definitions
includes(valueToFind: string, input: ReadonlyArray<string> | string): boolean;
includes(valueToFind: string): (input: ReadonlyArray<string> | string) => boolean;
includes<T>(valueToFind: T, input: ReadonlyArray<T>): boolean;
includes<T>(valueToFind: T): (input: ReadonlyArray<T>) => boolean;
Tests
import R from 'ramda'

import { includes } from './includes'

test('includes with string', () => {
  const str = 'more is less'

  expect(includes('less')(str)).toBeTrue()
  expect(R.includes('less')(str)).toBeTrue()
  expect(includes('never', str)).toBeFalse()
  expect(R.includes('never', str)).toBeFalse()
})

test('includes with array', () => {
  const arr = [ 1, 2, 3 ]

  expect(includes(2)(arr)).toBeTrue()
  expect(R.includes(2)(arr)).toBeTrue()

  expect(includes(4, arr)).toBeFalse()
  expect(R.includes(4, arr)).toBeFalse()
})

test('return false if input is falsy', () => {
  expect(includes(2, null)).toBeFalse()
  expect(() => R.includes(2, null)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of null')
  expect(includes(4, undefined)).toBeFalse()
  expect(() => R.includes(4, undefined)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of undefined')
})

indexBy

indexBy<T>(condition: (x: T) => string, list: ReadonlyArray<T>): { [key: string]: T }

It generates object with properties provided by condition and values provided by list array.

If condition is a function, then all list members are passed through it.

If condition is a string, then all list members are passed through R.path(condition).

const list = [ {id: 10}, {id: 20} ]

const withFunction = R.indexBy(
  x => x.id,
  list
)
const withString = R.indexBy(
  'id',
  list
)
const result = [
  withFunction, 
  R.equals(withFunction, withString)
]
// => [ { 10: {id: 10}, 20: {id: 20} }, true ]

Try the above R.indexBy example in Rambda REPL

All Typescript definitions
indexBy<T>(condition: (x: T) => string, list: ReadonlyArray<T>): { [key: string]: T };
indexBy<T>(condition: string, list: ReadonlyArray<T>): { [key: string]: T };
indexBy<T>(condition: (x: T) => string): (list: ReadonlyArray<T>) => { [key: string]: T };
indexBy<T>(condition: string): (list: ReadonlyArray<T>) => { [key: string]: T };
Tests
import { indexBy } from './indexBy'
import { prop } from './prop'

test('happy', () => {
  const list = [
    { id : 1 },
    {
      id : 1,
      a  : 2,
    },
    { id : 2 },
    { id : 10 },
    { id : 'a' },
  ]

  expect(indexBy(prop('id'))(list)).toEqual({
    1 : {
      id : 1,
      a  : 2,
    },
    2  : { id : 2 },
    10 : { id : 10 },
    a  : { id : 'a' },
  })
})

test('with string as condition', () => {
  const list = [ { id : 1 }, { id : 2 }, { id : 10 }, { id : 'a' } ]
  const standardResult = indexBy(obj => obj.id, list)
  const suggestionResult = indexBy('id', list)

  expect(standardResult).toEqual(suggestionResult)
})

test('with string - bad path', () => {
  const list = [
    {
      a : {
        b : 1,
        c : 2,
      },
    },
    { a : { c : 4 } },
    {},
    {
      a : {
        b : 10,
        c : 20,
      },
    },
  ]

  const result = indexBy('a.b', list)
  const expected = {
    1 : {
      a : {
        b : 1,
        c : 2,
      },
    },
    10 : {
      a : {
        b : 10,
        c : 20,
      },
    },
    undefined : {},
  }

  expect(result).toEqual(expected)
})

indexOf

indexOf<T>(valueToFind: T, list: ReadonlyArray<T>): number

It returns the index of the first element of list equals to valueToFind.

If there is no such element, it returns -1.

const list = [0, 1, 2, 3]

const result = [
  R.indexOf(2, list),
  R.indexOf(0, list)
]
// => [2, -1]

Try the above R.indexOf example in Rambda REPL

All Typescript definitions
indexOf<T>(valueToFind: T, list: ReadonlyArray<T>): number;
indexOf<T>(valueToFind: T): (list: ReadonlyArray<T>) => number;
Tests
import { indexOf } from './indexOf'

test('happy', () => {
  expect(indexOf(3, [ 1, 2, 3, 4 ])).toEqual(2)

  expect(indexOf(10)([ 1, 2, 3, 4 ])).toEqual(-1)
})

init

init<T>(listOrString: ReadonlyArray<T>): T[]

It returns all but the last element of listOrString.

const result = [
  R.init([1, 2, 3]) , 
  R.init('foo')  // => 'fo'
]
// => [[1, 2], 'fo']

Try the above R.init example in Rambda REPL

All Typescript definitions
init<T>(listOrString: ReadonlyArray<T>): T[];
init(listOrString: string): string;
Tests
import { init } from './init'

test('with array', () => {
  expect(init([ 1, 2, 3 ])).toEqual([ 1, 2 ])
  expect(init([ 1, 2 ])).toEqual([ 1 ])
  expect(init([ 1 ])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([ 1 ])).toEqual([])
})

test('with string', () => {
  expect(init('foo')).toEqual('fo')
  expect(init('f')).toEqual('')
  expect(init('')).toEqual('')
})

intersection

intersection<T>(listA: ReadonlyArray<T>, listB: ReadonlyArray<T>): T[]

It loops throw listA and listB and returns the intersection of the two according to R.equals.

const listA = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
const listB = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]

const result = intersection(listA, listB)
// => [{ id : 3 }, { id : 4 }]

Try the above R.intersection example in Rambda REPL

All Typescript definitions
intersection<T>(listA: ReadonlyArray<T>, listB: ReadonlyArray<T>): T[];
intersection<T>(listA: ReadonlyArray<T>): (listB: ReadonlyArray<T>) => T[];
Tests
import { intersection } from './intersection'

test('intersection', () => {
  const list1 = [ 1, 2, 3, 4 ]
  const list2 = [ 3, 4, 5, 6 ]
  expect(intersection(list1)(list2)).toEqual([ 3, 4 ])

  expect(intersection([], [])).toEqual([])
})

test('intersection with objects', () => {
  const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(intersection(list1)(list2)).toEqual([ { id : 3 }, { id : 4 } ])
})

intersperse

intersperse<T>(separator: T, list: ReadonlyArray<T>): T[]

It adds a separator between members of list.

const list = [ 0, 1, 2, 3 ]
const separator = '|'
const result = intersperse(separator, list)
// => [0, '|', 1, '|', 2, '|', 3]

Try the above R.intersperse example in Rambda REPL

All Typescript definitions
intersperse<T>(separator: T, list: ReadonlyArray<T>): T[];
intersperse<T>(separator: T): (list: ReadonlyArray<T>) => T[];
Tests
import { intersperse } from './intersperse'

test('intersperse', () => {
  const list = [ { id : 1 }, { id : 2 }, { id : 10 }, { id : 'a' } ]
  expect(intersperse('!', list)).toEqual([
    { id : 1 },
    '!',
    { id : 2 },
    '!',
    { id : 10 },
    '!',
    { id : 'a' },
  ])

  expect(intersperse('!')([])).toEqual([])
})

is

is(targetPrototype: any, x: any): boolean

It returns true if x is instance of targetPrototype.

const result = [
  R.is(String, 'foo'),  
  R.is(Array, 1)
]
// => [true, false]

Try the above R.is example in Rambda REPL

All Typescript definitions
is(targetPrototype: any, x: any): boolean;
is(targetPrototype: any): (x: any) => boolean;
Tests
import { is } from './is'

test('works with built-in types', () => {
  expect(is(Array, undefined)).toBeFalse()
  expect(is(Array)([])).toBeTrue()
  expect(is(Boolean, new Boolean(false))).toBeTrue()
  expect(is(Date, new Date())).toBeTrue()
  expect(is(Function, () => {})).toBeTrue()
  expect(is(Number, new Number(0))).toBeTrue()
  expect(is(Object, {})).toBeTrue()
  expect(is(RegExp, /(?:)/)).toBeTrue()
  expect(is(String, new String(''))).toBeTrue()
})

test('works with user-defined types', () => {
  function Foo(){}
  function Bar(){}
  Bar.prototype = new Foo()

  const foo = new Foo()
  const bar = new Bar()

  expect(is(Foo, foo)).toBeTrue()
  expect(is(Bar, bar)).toBeTrue()
  expect(is(Foo, bar)).toBeTrue()
  expect(is(Bar, foo)).toBeFalse()
})

test('does not coerce', () => {
  expect(is(Boolean, 1)).toBeFalse()
  expect(is(Number, '1')).toBeFalse()
  expect(is(Number, false)).toBeFalse()
})

test('recognizes primitives as their object equivalents', () => {
  expect(is(Boolean, false)).toBeTrue()
  expect(is(Number, 0)).toBeTrue()
  expect(is(String, '')).toBeTrue()
})

test('does not consider primitives to be instances of Object', () => {
  expect(is(Object, false)).toBeFalse()
  expect(is(Object, 0)).toBeFalse()
  expect(is(Object, '')).toBeFalse()
})

isEmpty

isEmpty<T>(x: T): boolean

It returns true if x is empty.

const result = [
  R.isEmpty(''),
  R.isEmpty({ x : 0 })
]
// => [true, false]

Try the above R.isEmpty example in Rambda REPL

All Typescript definitions
isEmpty<T>(x: T): boolean;
Tests
import { isEmpty } from './isEmpty'

test('happy', () => {
  expect(isEmpty(undefined)).toEqual(false)
  expect(isEmpty('')).toEqual(true)
  expect(isEmpty(null)).toEqual(false)
  expect(isEmpty(' ')).toEqual(false)
  expect(isEmpty(new RegExp(''))).toEqual(false)
  expect(isEmpty([])).toEqual(true)
  expect(isEmpty([ [] ])).toEqual(false)
  expect(isEmpty({})).toEqual(true)
  expect(isEmpty({ x : 0 })).toEqual(false)
  expect(isEmpty(0)).toEqual(false)
  expect(isEmpty(NaN)).toEqual(false)
  expect(isEmpty([ '' ])).toEqual(false)
})

isFunction

isFunction(input: any): boolean

It returns true if R.type of input is Async or Function.

const result = [
  R.isFunction(R.mapAsync),
  R.isFunction(R.add),
]
// => [true, true]

Try the above R.isFunction example in Rambda REPL

All Typescript definitions
isFunction(input: any): boolean;
Tests
import { isFunction } from './isFunction'

test('when function', () => {
  const fn = () => {}

  expect(isFunction(fn)).toEqual(true)
})

test('when promise', () => {
  const fn = Promise.resolve(2)

  expect(isFunction(fn)).toBeFalse()
})

test('when async', () => {
  const fn = async x => x

  expect(isFunction(fn)).toEqual(true)
})

test('when false', () => {
  expect(isFunction(null)).toEqual(false)
})

isNil

isNil(x: any): x is null | undefined

It returns true if x is either null or undefined.

const result = [
  R.isNil(null),
  R.isNil(1),
]
// => [true, false]

Try the above R.isNil example in Rambda REPL

All Typescript definitions
isNil(x: any): x is null | undefined;
Tests
import { isNil } from './isNil'

test('happy', () => {
  expect(isNil(null)).toBeTrue()

  expect(isNil(undefined)).toBeTrue()

  expect(isNil([])).toBeFalse()
})

isPromise

isPromise(input: any): boolean
All Typescript definitions
isPromise(input: any): boolean;

isType

isType(targetType: RambdaTypes, input: any): boolean

It returns true if targetType is equal to type of input according to R.type.

R.isType('Async',R.delay(1000))
// => true

Try the above R.isType example in Rambda REPL

All Typescript definitions
isType(targetType: RambdaTypes, input: any): boolean;
isType(targetType: RambdaTypes): (input: any) => boolean;
Tests
import { isType } from './isType'

const list = [ 1, 2, 3 ]

test('array', () => {
  expect(isType('Array', list)).toBeTruthy()
  expect(isType('Array')([])).toBeTruthy()
})

test('promise', () => {
  expect(isType('Promise', Promise.resolve(1))).toBeTruthy()
})

isValid

isValid({input: object, schema: Schema}): boolean

It checks if input is following schema specifications.

If validation fails, it returns false.

Please check the detailed explanation as it is hard to write a short description for this method.

const input = {a: ['foo', 'bar']}
const invalidInput = {a: ['foo', 'bar', 1]}
const schema = {a: [String]}
const result = [
  R.isValid({schema, input}),
  R.isValid({schema, input: invalidInput})
]
// => [true, false]

Try the above R.isValid example in Rambda REPL

All Typescript definitions
isValid({input: object, schema: Schema}): boolean;
Tests
import { delay } from './delay'
import { isPrototype, isValid } from './isValid'

test('is prototype', () => {
  expect(isPrototype(Promise)).toBeTrue()
  expect(isPrototype(Number)).toBeTrue()
  expect(isPrototype(Boolean)).toBeTrue()
  expect(isPrototype(String)).toBeTrue()
  expect(isPrototype(0)).toBeFalse()
})

test('prototype inside array', () => {
  const input = { a : [ 1, 2, 3, 4 ] }
  const schema = { a : [ Number ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('with Promise prototype', () => {
  const input = { a : [ delay(1), delay(2) ] }
  const schema = { a : [ Promise ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('object prototype as rule - true', () => {
  const input = { a : {} }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('list of functions', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ 'function' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function schema type can be only string', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ Function ] }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('object prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('number prototype as rule - true', () => {
  const input = { a : 1 }
  const schema = { a : Number }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - true', () => {
  const input = { a : [ 1, 2, 3 ] }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('string prototype as rule - true', () => {
  const input = { a : 'foo' }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('string prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('boolean prototype as rule - true', () => {
  const input = { a : true }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('boolean prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex prototype cannot be rule - true', () => {
  const input = { a : /foo/g }
  const schema = { a : new RegExp('foo') }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('undefined as a rule - true', () => {
  const input = { a : undefined }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('undefined as a rule - false', () => {
  const input = { a : null }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('null as a rule - true', () => {
  const input = { a : null }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('null as a rule - false', () => {
  const input = { a : undefined }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `null`', () => {
  const input = { a : null }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `undefined`', () => {
  const input = { a : undefined }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('type can be `"any"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `"function"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'function' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `async`', () => {
  const input = { a : async () => {} }
  const schema = { a : 'async' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise`', () => {
  const input = { a : delay(1999) }
  const schema = { a : 'promise' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise` list', () => {
  const input = { a : [ delay(1999) ] }
  const schema = { a : [ 'promise' ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function as schema - false', () => {
  const input = {
    a : {
      ab : () => true,
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('regex !ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /ba/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props is missing', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is missing - nested', () => {
  const input = {
    a : { ab : 'foo' },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 'bar',
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('nested schema', () => {
  const input = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 'foo',
  }
  const schema = {
    a : {
      b : 'string',
      c : 'number',
      d : 'string',
    },
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInputFirst = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()

  const invalidInputSecond = {
    a : {
      b : 'str',
      c : 'str',
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()

  const invalidInputThird = {
    a : { b : 'str' },
    b : 5,
  }

  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('array of type', () => {
  const input = {
    a : [ 1, 2 ],
    b : 'foo',
  }
  const schema = {
    a : [ 'number' ],
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInput = {
    a : [ 1, '1' ],
    b : 'foo',
  }

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('function as rule', () => {
  const input = {
    a : [ 1, 2, 3, 4 ],
    b : 'foo',
  }
  const invalidInput = {
    a : [ 4 ],
    b : 'foo',
  }

  const schema = {
    a : x => x.length > 2,
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('input prop is undefined', () => {
  const input = { b : 3 }
  const schema = { a : 'number' }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('enum', () => {
  const input = { a : 'foo' }
  const invalidInput = { a : '' }

  const schema = { a : [ 'foo', 'bar', 'baz' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('readme example', () => {
  const basicSchema = { a : [ 'string' ] }
  const schema = {
    b : [ basicSchema ],
    c : {
      d : { e : 'boolean' },
      f : 'array',
    },
    g : [ 'foo', 'bar', 'baz' ],
  }
  const input = {
    b : [ { a : [ 'led', 'zeppelin' ] } ],
    c : {
      d : { e : true },
      f : [ 'any', 1, null, 'value' ],
    },
    g : 'foo',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('should allow additional properties', () => {
  const input = {
    title : 'You shook me',
    year  : 1969,
  }

  expect(isValid({
    input,
    schema : { title : 'string' },
  })).toBeTruthy()
})

test('accepts values as schemas', () => {
  const input = {
    title : 'You shook me',
    genre : 'Blues',
    year  : 1969,
  }
  const schema = {
    title : 'You shook me',
    year  : 1969,
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('compatible schemas with nested object', () => {
  const input = {
    foo : 'bar',
    baz : { a : { b : 'c' } },
  }
  const invalidInputFirst = {
    foo : 'bar',
    baz : { a : { b : 1 } },
  }
  const invalidInputSecond = {
    foo : 'bar',
    baz : { a : { b : [] } },
  }
  const invalidInputThird = {
    foo : 'bar',
    baz : { a : { b : null } },
  }
  const schema = {
    foo : 'string',
    baz : { a : { b : 'string' } },
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('should return true when schema is empty object', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : {},
  })).toBeTruthy()
})

test('when schema is undefined', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : undefined,
  })).toBeFalsy()
})

test('should return false with invalid schema rule', () => {
  const input = {
    foo : 'bar',
    a   : {},
  }
  const inputSecond = { foo : 'bar' }

  const schema = {
    foo : 'string',
    baz : { a : {} },
  }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()

  expect(isValid({
    input : inputSecond,
    schema,
  })).toBeFalsy()
})

test('array of schemas', () => {
  const input = {
    b : [
      {
        a : 'led',
        b : 1,
      },
      {
        a : 'dancing',
        b : 1,
      },
    ],
  }
  const basicSchema = {
    a : String,
    b : Number,
  }
  const schema = { b : [ basicSchema ] }
  const result = isValid({
    input,
    schema,
  })

  expect(result).toBeTruthy()
})

isValidAsync

isValidAsync(x: IsValidAsync): Promise<boolean>

Asynchronous version of R.isValid

const input = {a: 1, b: 2}
const invalidInput = {a: 1, b: 'foo'}
const schema = {a: Number, b: async x => {
  await R.delay(100)
  return typeof x === 'number'
}}

const result = await Promise.all([
  R.isValid({schema, input}),
  R.isValid({schema, input: invalidInput})
])
// => [true, false]

Try the above R.isValidAsync example in Rambda REPL

All Typescript definitions
isValidAsync(x: IsValidAsync): Promise<boolean>;
Tests
import { result } from 'lodash'

import { delay } from './delay'
import { isValidAsync } from './isValidAsync'

const simplePredicate = async x => {
  await delay(100)

  return x > 5
}

test('happy', async () => {
  const input = {
    a          : 1,
    b          : 7,
    c          : 9,
    additional : 'foo',
  }
  const invalidInput = {
    a : 1,
    b : 2,
    c : 9,
  }
  const schema = {
    a : Number,
    b : simplePredicate,
    c : simplePredicate,
  }
  const invalidSchema = {
    a : Boolean,
    b : simplePredicate,
    c : simplePredicate,
  }
  const result = await isValidAsync({
    input,
    schema,
  })
  const invalidResult = await isValidAsync({
    input,
    schema : invalidSchema,
  })
  const withInvalidInput = await isValidAsync({
    input : invalidInput,
    schema,
  })
  expect(result).toBeTruthy()
  expect(invalidResult).toBeFalsy()
  expect(withInvalidInput).toBeFalsy()
})

test('without async rules', async () => {
  const input = {
    a : 1,
    b : 7,
  }
  const schema = {
    a : Number,
    b : x => x > 2,
  }
  const invalidSchema = {
    a : Number,
    b : Boolean,
  }
  const result = await isValidAsync({
    input,
    schema,
  })
  const invalidResult = await isValidAsync({
    input,
    schema : invalidSchema,
  })

  expect(result).toBeTruthy()
  expect(invalidResult).toBeFalsy()
})

test('readme example', async () => {
  const input = {
    a : 1,
    b : 2,
  }
  const invalidInput = {
    a : 1,
    b : 'foo',
  }
  const schema = {
    a : Number,
    b : async x => {
      await delay(100)

      return typeof x === 'number'
    },
  }
  const result = await Promise.all([
    isValidAsync({
      schema,
      input,
    }),
    isValidAsync({
      schema,
      input : invalidInput,
    }),
  ])
  expect(result).toEqual([ true, false ])
})

join

join<T>(glue: string, list: ReadonlyArray<T>): string

It returns a string of all list instances joined with a glue.

R.join('-', [1, 2, 3])  // => '1-2-3'

Try the above R.join example in Rambda REPL

All Typescript definitions
join<T>(glue: string, list: ReadonlyArray<T>): string;
join<T>(glue: string): (list: ReadonlyArray<T>) => string;
Tests
import { join } from './join'

test('curry', () => {
  expect(join('|')([ 'foo', 'bar', 'baz' ])).toEqual('foo|bar|baz')

  expect(join('|', [ 1, 2, 3 ])).toEqual('1|2|3')

  const spacer = join(' ')

  expect(spacer([ 'a', 2, 3.4 ])).toEqual('a 2 3.4')
})

keys

keys<T extends object>(x: T): (keyof T)[]

It applies Object.keys over x and returns its keys.

R.keys({a:1, b:2})  // => ['a', 'b']

Try the above R.keys example in Rambda REPL

All Typescript definitions
keys<T extends object>(x: T): (keyof T)[];
keys<T>(x: T): string[];
Tests
import { keys } from './keys'

test('happy', () => {
  expect(keys({ a : 1 })).toEqual([ 'a' ])
})

last

last(str: string): string

It returns the last element of input, as the input can be either a string or an array.

const result = [
  R.last([1, 2, 3]),
  R.last('foo'),
]
// => [3, 'o']

Try the above R.last example in Rambda REPL

All Typescript definitions
last(str: string): string;
last(emptyList: readonly []): undefined;
last<T extends any>(list: readonly T[]): T | undefined;
Tests
import { last } from './last'

test('happy', () => {
  expect(last([ 'foo', 'bar', 'baz' ])).toEqual('baz')
  expect(last([])).toEqual(undefined)
  expect(last('abc')).toEqual('c')
  expect(last('')).toEqual('')
})

lastIndexOf

lastIndexOf<T>(target: T, list: ReadonlyArray<T>): number

It returns the last index of target in list array.

R.equals is used to determine equality between target and members of list.

If there is no such index, then -1 is returned.

const list = [1, 2, 3, 1, 2, 3]
const result = [
  R.lastIndexOf(2, list),
  R.lastIndexOf(4, list),
]
// => [4, -1]

Try the above R.lastIndexOf example in Rambda REPL

All Typescript definitions
lastIndexOf<T>(target: T, list: ReadonlyArray<T>): number;
lastIndexOf<T>(target: T): (list: ReadonlyArray<T>) => number;
Tests
import { lastIndexOf } from './lastIndexOf'

test('happy', () => {
  const a = lastIndexOf(1, [ 1, 2, 3, 1, 2 ])
  const b = lastIndexOf(1)([ 1, 2, 3, 1, 2 ])

  expect(a).toEqual(3)
  expect(b).toEqual(3)
})

test('false', () => {
  const a = lastIndexOf(10, [ 1, 2, 3, 1, 2 ])

  expect(a).toEqual(-1)
})

length

length<T>(listOrString: ReadonlyArray<T>): number

It returns the length property of listOrString.

const result = [
  R.length([1, 2, 3, 4]),
  R.length('foo'),
]
// => [4, 3]

Try the above R.length example in Rambda REPL

All Typescript definitions
length<T>(listOrString: ReadonlyArray<T>): number;
Tests
import { length } from './length'

test('happy', () => {
  expect(length('foo')).toEqual(3)
  expect(length([ 1, 2, 3 ])).toEqual(3)
  expect(length([])).toEqual(0)
})

test('with empty string', () => {
  expect(length('')).toEqual(0)
})

test('with bad input returns NaN', () => {
  expect(length(0)).toBeNaN()
  expect(length({})).toBeNaN()
  expect(length(null)).toBeNaN()
  expect(length(undefined)).toBeNaN()
})

lens

lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens

It returns a lens for the given getter and setter functions.

The getter gets the value of the focus; the setter sets the value of the focus.

The setter should not mutate the data structure.

const xLens = R.lens(R.prop('x'), R.assoc('x'));

R.view(xLens, {x: 1, y: 2}) // => 1
R.set(xLens, 4, {x: 1, y: 2}) // => {x: 4, y: 2}
R.over(xLens, R.negate, {x: 1, y: 2}) // => {x: -1, y: 2}

Try the above R.lens example in Rambda REPL

All Typescript definitions
lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens;
lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens;
Tests
import { assoc } from './assoc'
import { compose } from './compose'
import { lens } from './lens'
import { lensIndex } from './lensIndex'
import { lensPath } from './lensPath'
import { lensProp } from './lensProp'
import { over } from './over'
import { prop } from './prop'
import { set } from './set'
import { toUpper } from './toUpper'
import { view } from './view'

const alice = {
  name    : 'Alice Jones',
  address : [ '22 Walnut St', 'San Francisco', 'CA' ],
  pets    : {
    dog : 'joker',
    cat : 'batman',
  },
}

const nameLens = lens(prop('name'), assoc('name'))
const addressLens = lensProp('address')
const headLens = lensIndex(0)
const dogLens = lensPath('pets.dog')

test('view', () => {
  expect(view(nameLens, alice)).toEqual('Alice Jones')

  expect(view(dogLens, alice)).toEqual('joker')

  expect(view(headLens, alice.address)).toEqual('22 Walnut St')
})

test('over', () => {
  expect(over(
    nameLens, toUpper, alice
  )).toEqual({
    name    : 'ALICE JONES',
    address : [ '22 Walnut St', 'San Francisco', 'CA' ],
    pets    : {
      dog : 'joker',
      cat : 'batman',
    },
  })

  expect(over(
    dogLens, toUpper, alice
  )).toEqual({
    name    : 'Alice Jones',
    address : [ '22 Walnut St', 'San Francisco', 'CA' ],
    pets    : {
      dog : 'JOKER',
      cat : 'batman',
    },
  })

  expect(over(headLens, toUpper)(alice.address)).toEqual([
    '22 WALNUT ST',
    'San Francisco',
    'CA',
  ])
})

test('set', () => {
  expect(set(
    nameLens, 'Alice Smith', alice
  )).toEqual({
    name    : 'Alice Smith',
    address : [ '22 Walnut St', 'San Francisco', 'CA' ],
    pets    : {
      dog : 'joker',
      cat : 'batman',
    },
  })

  expect(set(
    dogLens, 'bane', alice
  )).toEqual({
    name    : 'Alice Jones',
    address : [ '22 Walnut St', 'San Francisco', 'CA' ],
    pets    : {
      dog : 'bane',
      cat : 'batman',
    },
  })

  expect(set(
    headLens, '52 Crane Ave', alice.address
  )).toEqual([
    '52 Crane Ave',
    'San Francisco',
    'CA',
  ])
})

test('composed lenses', () => {
  const composedStreetLens = compose(addressLens, headLens)
  const composedDogLens = compose(lensPath('pets'), lensPath('dog'))

  expect(view(composedDogLens, alice)).toEqual(view(dogLens, alice))

  expect(view(composedStreetLens, alice)).toEqual('22 Walnut St')

  expect(over(
    composedStreetLens, toUpper, alice
  )).toEqual({
    name    : 'Alice Jones',
    address : [ '22 WALNUT ST', 'San Francisco', 'CA' ],
    pets    : {
      dog : 'joker',
      cat : 'batman',
    },
  })

  expect(set(
    composedStreetLens, '52 Crane Ave', alice
  )).toEqual({
    name    : 'Alice Jones',
    address : [ '52 Crane Ave', 'San Francisco', 'CA' ],
    pets    : {
      dog : 'joker',
      cat : 'batman',
    },
  })
})

lensIndex

lensIndex(index: number): Lens

It returns a lens that focuses on specified index.

const list = ['a', 'b', 'c']
const headLens = R.lensIndex(0)

R.view(headLens, list) // => 'a'
R.set(headLens, 'x', list) // => ['x', 'b', 'c']
R.over(headLens, R.toUpper, list) // => ['A', 'b', 'c']

Try the above R.lensIndex example in Rambda REPL

All Typescript definitions
lensIndex(index: number): Lens;
Tests
import { compose } from './compose'
import { keys } from './keys'
import { lensIndex } from './lensIndex'
import { over } from './over'
import { set } from './set'
import { view } from './view'

const testList = [ { a : 1 }, { b : 2 }, { c : 3 } ]

test('focuses list element at the specified index', () => {
  expect(view(lensIndex(0), testList)).toEqual({ a : 1 })
})

test('returns undefined if the specified index does not exist', () => {
  expect(view(lensIndex(10), testList)).toEqual(undefined)
})

test('sets the list value at the specified index', () => {
  expect(set(
    lensIndex(0), 0, testList
  )).toEqual([ 0, { b : 2 }, { c : 3 } ])
})

test('applies function to the value at the specified list index', () => {
  expect(over(
    lensIndex(2), keys, testList
  )).toEqual([ { a : 1 }, { b : 2 }, [ 'c' ] ])
})

test('can be composed', () => {
  const nestedList = [ 0, [ 10, 11, 12 ], 1, 2 ]
  const composedLens = compose(lensIndex(1), lensIndex(0))

  expect(view(composedLens, nestedList)).toEqual(10)
})

test('set s (get s) === s', () => {
  expect(set(
    lensIndex(0), view(lensIndex(0), testList), testList
  )).toEqual(testList)
})

test('get (set s v) === v', () => {
  expect(view(lensIndex(0), set(
    lensIndex(0), 0, testList
  ))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensIndex(0),
    set(
      lensIndex(0), 11, set(
        lensIndex(0), 10, testList
      )
    ))).toEqual(11)
})

lensPath

lensPath(path: RamdaPath): Lens

It returns a lens that focuses on specified path.

const lensPath = R.lensPath(['x', 0, 'y'])
const input = {x: [{y: 2, z: 3}, {y: 4, z: 5}]}

R.view(lensPath, input) //=> 2

R.set(lensPath, 1, input) 
//=> {x: [{y: 1, z: 3}, {y: 4, z: 5}]}

R.over(xHeadYLens, R.negate, input) 
//=> {x: [{y: -2, z: 3}, {y: 4, z: 5}]}

Try the above R.lensPath example in Rambda REPL

All Typescript definitions
lensPath(path: RamdaPath): Lens;
Tests
import { compose } from './compose'
import { identity } from './identity'
import { inc } from './inc'
import { lensPath } from './lensPath'
import { lensProp } from './lensProp'
import { over } from './over'
import { set } from './set'
import { view } from './view'

const testObj = {
  a : [ { b : 1 }, { b : 2 } ],
  d : 3,
}

test('view', () => {
  expect(view(lensPath('d'), testObj)).toEqual(3)
  expect(view(lensPath('a.0.b'), testObj)).toEqual(1)
  // this is different to ramda, ramda will return a clone of the input object
  expect(view(lensPath(''), testObj)).toEqual(undefined)
})

test('set', () => {
  expect(set(
    lensProp('d'), 0, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 2 } ],
    d : 0,
  })
  expect(set(
    lensPath('a.0.b'), 0, testObj
  )).toEqual({
    a : [ { b : 0 }, { b : 2 } ],
    d : 3,
  })
  expect(set(
    lensPath('a.0.X'), 0, testObj
  )).toEqual({
    a : [
      {
        b : 1,
        X : 0,
      },
      { b : 2 },
    ],
    d : 3,
  })
  expect(set(
    lensPath([]), 0, testObj
  )).toEqual(0)
})

test('over', () => {
  expect(over(
    lensPath('d'), inc, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 2 } ],
    d : 4,
  })
  expect(over(
    lensPath('a.1.b'), inc, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 3 } ],
    d : 3,
  })
  expect(over(
    lensProp('X'), identity, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 2 } ],
    d : 3,
    X : undefined,
  })
  expect(over(
    lensPath('a.0.X'), identity, testObj
  )).toEqual({
    a : [
      {
        b : 1,
        X : undefined,
      },
      { b : 2 },
    ],
    d : 3,
  })
})

test('compose', () => {
  const composedLens = compose(lensPath('a'), lensPath('1.b'))
  expect(view(composedLens, testObj)).toEqual(2)
})

test('set s (get s) === s', () => {
  expect(set(
    lensPath([ 'd' ]), view(lensPath([ 'd' ]), testObj), testObj
  )).toEqual(testObj)
  expect(set(
    lensPath([ 'a', 0, 'b' ]),
    view(lensPath([ 'a', 0, 'b' ]), testObj),
    testObj
  )).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensPath([ 'd' ]), set(
    lensPath([ 'd' ]), 0, testObj
  ))).toEqual(0)
  expect(view(lensPath([ 'a', 0, 'b' ]), set(
    lensPath([ 'a', 0, 'b' ]), 0, testObj
  ))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  const p = [ 'd' ]
  const q = [ 'a', 0, 'b' ]
  expect(view(lensPath(p), set(
    lensPath(p), 11, set(
      lensPath(p), 10, testObj
    )
  ))).toEqual(11)
  expect(view(lensPath(q), set(
    lensPath(q), 11, set(
      lensPath(q), 10, testObj
    )
  ))).toEqual(11)
})

lensProp

lensProp(prop: string): {
  <T, U>(obj: T): U

It returns a lens that focuses on specified property prop.

const xLens = R.lensProp('x');
const input = {x: 1, y: 2}

R.view(xLens, input) // => 1

R.set(xLens, 4, input) 
// => {x: 4, y: 2}

R.over(xLens, R.negate, input) 
// => {x: -1, y: 2}

Try the above R.lensProp example in Rambda REPL

All Typescript definitions
lensProp(prop: string): {
  <T, U>(obj: T): U;
  set<T, U, V>(val: T, obj: U): V;
};
Tests
import { compose } from './compose'
import { identity } from './identity'
import { inc } from './inc'
import { lensProp } from './lensProp'
import { over } from './over'
import { set } from './set'
import { view } from './view'

const testObj = {
  a : 1,
  b : 2,
  c : 3,
}

test('focuses object the specified object property', () => {
  expect(view(lensProp('a'), testObj)).toEqual(1)
})

test('returns undefined if the specified property does not exist', () => {
  expect(view(lensProp('X'), testObj)).toEqual(undefined)
})

test('sets the value of the object property specified', () => {
  expect(set(
    lensProp('a'), 0, testObj
  )).toEqual({
    a : 0,
    b : 2,
    c : 3,
  })
})

test('adds the property to the object if it doesn\'t exist', () => {
  expect(set(
    lensProp('d'), 4, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  })
})

test('applies function to the value of the specified object property', () => {
  expect(over(
    lensProp('a'), inc, testObj
  )).toEqual({
    a : 2,
    b : 2,
    c : 3,
  })
})

test('applies function to undefined and adds the property if it doesn\'t exist', () => {
  expect(over(
    lensProp('X'), identity, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    X : undefined,
  })
})

test('can be composed', () => {
  const nestedObj = {
    a : { b : 1 },
    c : 2,
  }
  const composedLens = compose(lensProp('a'), lensProp('b'))

  expect(view(composedLens, nestedObj)).toEqual(1)
})

test('set s (get s) === s', () => {
  expect(set(
    lensProp('a'), view(lensProp('a'), testObj), testObj
  )).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensProp('a'), set(
    lensProp('a'), 0, testObj
  ))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensProp('a'),
    set(
      lensProp('a'), 11, set(
        lensProp('a'), 10, testObj
      )
    ))).toEqual(11)
})

map

map<T, U>(fn: MapFunctionObject<T, U>, list: Dictionary<T>): Dictionary<U>

It returns the result of looping through list with fn.

It works with both array and object.

const fn = (x, i) => (x * 2) + i
const fnWhenObject = (val, prop)=>{
  return `${prop}-${val}`
}

const list = [1, 2]
const obj = {a: 1, b: 2}

const result = [ 
  R.map(fn, list),
  R.map(fnWhenObject, obj)
]
// => [ [2, 5], {a: 'a-1', b: 'b-2'}]

Try the above R.map example in Rambda REPL

All Typescript definitions
map<T, U>(fn: MapFunctionObject<T, U>, list: Dictionary<T>): Dictionary<U>;
map<T, U>(fn: MapFunctionArray<T, U>, list: T[]): U[];
map<T, U>(fn: MapFunctionArray<T, U>): (list: T[]) => U[];
map<T, U, S>(fn: MapFunctionObject<T, U>): (list: Dictionary<T>) => Dictionary<U>;
map<T>(fn: MapFunctionArray<T, T>): (list: T[]) => T[];
map<T>(fn: MapFunctionArray<T, T>, list: ReadonlyArray<T>): T[];
Tests
import { map } from './map'

const double = x => x * 2

const sampleObject = {
  a : 1,
  b : 2,
  c : 3,
  d : 4,
}

test('with array', () => {
  expect(map(double, [ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
})

test('pass index as second argument', () => {
  map((x, i) => {
    expect(i).toBeNumber()
  },
  [ 10, 20, 30 ])
})

test('with object', () => {
  const obj = {
    a : 1,
    b : 2,
  }

  expect(map(double, obj)).toEqual({
    a : 2,
    b : 4,
  })
})

test('pass input object as third argument', () => {
  const obj = {
    a : 1,
    b : 2,
  }
  const iterator = (
    val, prop, inputObject
  ) => {
    expect(inputObject).toEqual(obj)

    return val * 2
  }

  expect(map(iterator, obj)).toEqual({
    a : 2,
    b : 4,
  })
})

test('with object passes property as second argument', () => {
  map((_, prop) => {
    expect(typeof prop).toEqual('string')
  })(sampleObject)
})

/**
 * https://github.com/selfrefactor/rambda/issues/77
 */
test('when undefined instead of array', () => {
  expect(map(double, undefined)).toEqual([])
})

mapAsync

mapAsync<T, K>(fn: AsyncIterable<T, K>, list: T[]): Promise<K[]>

Sequential asynchronous mapping with fn over members of list.

async function fn(x){
  await R.delay(1000)

  return x+1
}

const result = R.mapAsync(fn, [1, 2, 3])
// `result` resolves after 3 seconds to `[2, 3, 4]`

Try the above R.mapAsync example in Rambda REPL

All Typescript definitions
mapAsync<T, K>(fn: AsyncIterable<T, K>, list: T[]): Promise<K[]>;
mapAsync<T, K>(fn: AsyncIterableIndexed<T, K>, list: T[]): Promise<K[]>;
mapAsync<T, K>(fn: AsyncIterable<T, K>) : ( list: T[]) => Promise<K[]>;
mapAsync<T, K>(fn: AsyncIterableIndexed<T, K>) : ( list: T[]) => Promise<K[]>;
Tests
import { composeAsync } from './composeAsync'
import { map } from './map'
import { mapAsync } from './mapAsync'

const delay = a =>
  new Promise(resolve => {
    setTimeout(() => {
      resolve(a + 20)
    }, 100)
  })

const tap = a =>
  new Promise(resolve => {
    setTimeout(() => {
      resolve(a)
    }, 100)
  })

const rejectDelay = a =>
  new Promise((_, reject) => {
    setTimeout(() => {
      reject(a + 20)
    }, 100)
  })

test('', async () => {
  const result = await mapAsync(delay, [ 1, 2, 3 ])
  expect(result).toEqual([ 21, 22, 23 ])
})

test('with object', async () => {
  const result = await mapAsync(delay, {
    a : 1,
    b : 2,
    c : 3,
  })
  expect(result).toEqual({
    a : 21,
    b : 22,
    c : 23,
  })
})

test('with array', async () => {
  await mapAsync((x, i) => {
    expect(x % 10).toBe(0)
    expect(typeof i).toBe('number')
  },
  [ 10, 20, 30 ])
})

test('composeAsync', async () => {
  const result = await composeAsync(
    mapAsync(delay),
    mapAsync(async a => delay(a)),
    map(a => a * 10)
  )(await tap([ 1, 2, 3 ]))
  expect(result).toEqual([ 50, 60, 70 ])
})

test('error', async () => {
  try {
    await mapAsync(rejectDelay)([ 1, 2, 3 ])
  } catch (err){
    expect(err).toBe(21)
  }
})

mapAsyncLimit

mapAsyncLimit<T, K>(fn: AsyncIterable<T, K>, limit: number, list: T[]): Promise<K[]>

It is similar to R.mapFastAsync in that it uses Promise.all but not over the whole list, rather than with only slice from list with length limit.

All Typescript definitions
mapAsyncLimit<T, K>(fn: AsyncIterable<T, K>, limit: number, list: T[]): Promise<K[]>;
mapAsyncLimit<T, K>(fn: AsyncIterableIndexed<T, K>, limit: number, list: T[]): Promise<K[]>;
Tests
import isCI from 'is-ci'

import { composeAsync } from './composeAsync'
import { delay } from './delay'
import { mapAsync } from './mapAsync'
import { mapAsyncLimit } from './mapAsyncLimit'
import { toDecimal } from './toDecimal'

jest.setTimeout(30000)

test('happy', async () => {
  const limit = 3
  const startTime = new Date().getTime()
  const list = [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
  const iterable = async x => {
    await delay(500)

    return x + 1
  }
  const result = await mapAsyncLimit(
    iterable, limit, list
  )
  const endTime = new Date().getTime()
  const diffTime = endTime - startTime

  const startTime2 = new Date().getTime()
  await mapAsync(iterable, list)
  const endTime2 = new Date().getTime()
  const diffTime2 = endTime2 - startTime2

  const methodScale = toDecimal((diffTime2 - diffTime) / 1000, 0)
  expect(result).toEqual([ 2, 3, 4, 5, 6, 7, 8, 9, 10 ])
  if (!isCI) expect(methodScale).toBe(limit)
})

mapFastAsync

mapFastAsync<T, K>(fn: AsyncIterable<T, K>, list: T[]): Promise<K[]>

Parrallel asynchronous mapping with fn over members of list.

async function fn(x){
  await R.delay(1000)

  return x+1
}

const result = R.mapFastAsync(fn, [1, 2, 3])
// `result` resolves after 1 second to `[2, 3, 4]`

Try the above R.mapFastAsync example in Rambda REPL

All Typescript definitions
mapFastAsync<T, K>(fn: AsyncIterable<T, K>, list: T[]): Promise<K[]>;
mapFastAsync<T, K>(fn: AsyncIterableIndexed<T, K>, list: T[]): Promise<K[]>;
mapFastAsync<T, K>(fn: AsyncIterable<T, K>) : ( list: T[]) => Promise<K[]>;
mapFastAsync<T, K>(fn: AsyncIterableIndexed<T, K>) : ( list: T[]) => Promise<K[]>;
Tests
import { composeAsync } from './composeAsync'
import { delay } from './delay'
import { map } from './map'
import { mapFastAsync } from './mapFastAsync'

test('happy', async () => {
  const fn = async x => {
    await delay(100)

    return x + 10
  }
  const result = await mapFastAsync(fn, [ 1, 2, 3 ])
  const curriedResult = await mapFastAsync(fn)([ 1, 2, 3 ])
  expect(result).toEqual([ 11, 12, 13 ])
  expect(curriedResult).toEqual([ 11, 12, 13 ])
})

test('composeAsync', async () => {
  const result = await composeAsync(
    mapFastAsync(async x => {
      await delay(100)

      return x + 1
    }),
    mapFastAsync(async x => {
      await delay(100)

      return x + 10
    }),
    map(x => x * 10)
  )([ 1, 2, 3 ])
  expect(result).toEqual([ 21, 31, 41 ])
})

test('error', async () => {
  try {
    const fn = async x => {
      JSON.parse('{:')
    }
    const result = await mapFastAsync(fn, [ 1, 2, 3 ])
  } catch (err){
    expect(err.message).toBe('Unexpected token : in JSON at position 1')
  }
})

test('pass index as second argument', async () => {
  await mapFastAsync((x, i) => {
    expect(x % 10).toBe(0)
    expect(typeof i).toBe('number')
  },
  [ 10, 20, 30 ])
})

mapToObject

mapToObject<T, U>(fn: (input: T) => object|false, list: T[]): U

This method allows to generate an object from a list using input function fn.

This function must return either an object or false for every member of list input.

If false is returned, then this element of list will be skipped in the calculation of the result.

All of returned objects will be merged to generate the final result.

const list = [1, 2, 3, 12]
const fn = x => {
  if(x > 10) return false
  return x % 2 ? {[x]: x + 1}: {[x]: x + 10}
}

const result = mapToObject(fn, list)
const expected = {'1': 2, '2': 12, '3': 4}
// => `result` is equal to `expected`

Try the above R.mapToObject example in Rambda REPL

All Typescript definitions
mapToObject<T, U>(fn: (input: T) => object|false, list: T[]): U;
mapToObject<T, U>(fn: (input: T) => object|false): (list: T[]) => U;
Tests
import { mapToObject } from './mapToObject'

const list = [ 1, 2, 3 ]
const fn = x => x % 2 ? { [ x ] : x + 1 } : { [ x ] : x + 10 }
const expected = {
  1 : 2,
  2 : 12,
  3 : 4,
}

test('happy', () => {
  const result = mapToObject(fn, list)
  expect(result).toEqual(expected)
})

test('curried', () => {
  const result = mapToObject(fn)(list)
  expect(result).toEqual(expected)
})

test('string.fn test', () => {
  const list = [ 'auto', 'bar=false', 'foo', 'baz=1.5', 's=more', 'k=2' ]
  const fn = x => {
    const [ key, value ] = x.split('=')
    if (value === undefined || value === 'true'){
      return { [ key ] : true }
    }
    if (value === 'false'){
      return { [ key ] : false }
    }

    if (Number.isNaN(Number(value))){
      return { [ key ] : value }
    }

    return { [ key ] : Number(value) }
  }

  const expectedResult = {
    auto : true,
    foo  : true,
    bar  : false,
    baz  : 1.5,
    s    : 'more',
    k    : 2,
  }
  const result = mapToObject(fn, list)

  expect(result).toEqual(expectedResult)
})

test('bad path', () => {
  expect(() => mapToObject(1, null)).toThrow()
})

mapToObjectAsync

mapToObjectAsync<T, U>(fn: (input: T) => Promise<object|false>, list: T[]): Promise<U>

Asynchronous version of R.mapToObject

All Typescript definitions
mapToObjectAsync<T, U>(fn: (input: T) => Promise<object|false>, list: T[]): Promise<U>;
Tests
import { delay } from './delay'
import { mapToObjectAsync } from './mapToObjectAsync'

const list = [ 1, 2, 3, 12 ]
const fn = async x => {
  await delay(100)
  if (x > 10) return false

  return x % 2 ? { [ `key${ x }` ] : x + 1 } : { [ `key${ x }` ] : x + 10 }
}

const expected = {
  key1 : 2,
  key2 : 12,
  key3 : 4,
}

test('happy', async () => {
  const result = await mapToObjectAsync(fn, list)
  expect(result).toEqual(expected)
})

match

match(regExpression: RegExp, str: string): string[]

Curried version of String.prototype.match which returns empty array, when there is no match.

const result = [
  R.match('a', 'foo'),
  R.match(/([a-z]a)/g, 'bananas')
]
// => [[], ['ba', 'na', 'na']]

Try the above R.match example in Rambda REPL

All Typescript definitions
match(regExpression: RegExp, str: string): string[];
match(regExpression: RegExp): (str: string) => string[];
Tests
import { equals } from './equals'
import { match } from './match'

test('happy', () => {
  expect(match(/a./g)('foo bar baz')).toEqual([ 'ar', 'az' ])
})

test('fallback', () => {
  expect(match(/a./g)('foo')).toEqual([])
})

test('with string', () => {
  expect(match('a', 'foo')).toEqual([])
  expect(equals(match('o', 'foo'), [ 'o' ])).toBeTrue()
})

test('throwing', () => {
  expect(() => {
    match(/a./g, null)
  }).toThrowWithMessage(TypeError, 'Cannot read property \'match\' of null')
})

mathMod

mathMod(x: number, y: number): number

R.mathMod behaves like the modulo operator should mathematically, unlike the % operator (and by extension, R.modulo). So while -17 % 5 is -2, mathMod(-17, 5) is 3.

const result = [
  R.mathMod(-17, 5),
  R.mathMod(17, 5),
  R.mathMod(17, -5),  
  R.mathMod(17, 0)   
]
// => [3, 2, NaN, NaN]

Try the above R.mathMod example in Rambda REPL

All Typescript definitions
mathMod(x: number, y: number): number;
mathMod(x: number): (y: number) => number;
Tests
import { mathMod } from './mathMod'

test('happy', () => {
  expect(mathMod(-17)(5)).toEqual(3)
  expect(mathMod(17, 5)).toEqual(2)
  expect(mathMod(17, -5)).toBeNaN()
  expect(mathMod(17, 0)).toBeNaN()
  expect(mathMod('17', 5)).toBeNaN()
  expect(mathMod({}, 2)).toBeNaN()
  expect(mathMod([], 2)).toBeNaN()
  expect(mathMod(Symbol(), 2)).toBeNaN()
})

max

max<T extends Ord>(x: T, y: T): T

It returns the greater value between x and y.

const result = [
  R.max(5, 7),  
  R.max('bar', 'foo'),  
]
// => [7, 'foo']

Try the above R.max example in Rambda REPL

All Typescript definitions
max<T extends Ord>(x: T, y: T): T;
max<T extends Ord>(x: T): (y: T) => T;
Tests
import { max } from './max'

test('with number', () => {
  expect(max(2, 1)).toBe(2)
})

test('with string', () => {
  expect(max('foo')('bar')).toBe('foo')
  expect(max('bar')('baz')).toBe('baz')
})

maxBy

maxBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T

It returns the greater value between x and y according to compareFn function.

const compareFn = Math.abs

R.maxBy(compareFn, 5, -7) // => -7

Try the above R.maxBy example in Rambda REPL

All Typescript definitions
maxBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T;
maxBy<T>(compareFn: (input: T) => Ord, x: T): (y: T) => T;
maxBy<T>(compareFn: (input: T) => Ord): FunctionToolbelt.Curry<(x: T, y: T) => T>;
Tests
import { maxBy } from './maxBy'

test('happy', () => {
  expect(maxBy(
    Math.abs, -5, 2
  )).toEqual(-5)
})

test('curried', () => {
  expect(maxBy(Math.abs)(2, -5)).toEqual(-5)
  expect(maxBy(Math.abs)(2)(-5)).toEqual(-5)
})

maybe

maybe<T>(ifRule: boolean, whenIf: T | Func<T>, whenElse: T | Func<T>): T

It acts as ternary operator and it is helpful when we have nested ternaries.

All of the inputs can be either direct values or anonymous functions. This is helpful if we don't want to evaluate certain paths as we can wrap this logic in a function.

const x = 4
const y = 8

const ifRule = x > 2
const whenIf = y > 10 ? 3 : 7
const whenElse = () => {
  // just to show that it won't be evaluated
  return JSON.parse('{a:')
}

const result = R.maybe(
  ifRule,
  whenIf,
  whenElse,
)
// `result` is `7`

Try the above R.maybe example in Rambda REPL

All Typescript definitions
maybe<T>(ifRule: boolean, whenIf: T | Func<T>, whenElse: T | Func<T>): T;
maybe<T>(ifRule: VoidInputFunc<boolean>, whenIf: T | Func<T>, whenElse: T | Func<T>): T;
Tests
import { maybe } from './maybe'

const WHEN_IF = 'WHEN_IF'
const WHEN_ELSE = 'WHEN_ELSE'

test('prevent type error', () => {
  const x = 5
  const y = null
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, () => y.a === 'foo'
  )

  expect(result).toBe(WHEN_IF)
})

test('whenElse is a function', () => {
  const x = 2
  const y = { a : 1 }
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, () => y.a === 'foo'
  )

  expect(result).toBeFalse()
})

test('whenIf', () => {
  const x = 5
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, WHEN_ELSE
  )

  expect(result).toBe(WHEN_IF)
})

test('whenIf is a function', () => {
  const x = 5
  const ifRule = () => x > 3

  const result = maybe(
    ifRule, () => WHEN_IF, WHEN_ELSE
  )

  expect(result).toBe(WHEN_IF)
})

test('whenElse', () => {
  const x = 1
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, WHEN_ELSE
  )

  expect(result).toBe(WHEN_ELSE)
})

mean

mean(list: ReadonlyArray<number>): number

It returns the mean value of list input.

R.mean([ 2, 7 ])
// => 4.5

Try the above R.mean example in Rambda REPL

All Typescript definitions
mean(list: ReadonlyArray<number>): number;
Tests
import { mean } from './mean'

test('happy', () => {
  expect(mean([ 2, 7 ])).toBe(4.5)
})

test('with NaN', () => {
  expect(mean([])).toBeNaN()
})

median

median(list: ReadonlyArray<number>): number

It returns the median value of list input.

R.median([ 7, 2, 10, 9 ]) // => 8

Try the above R.median example in Rambda REPL

All Typescript definitions
median(list: ReadonlyArray<number>): number;
Tests
import { median } from './median'

test('happy', () => {
  expect(median([ 2 ])).toEqual(2)
  expect(median([ 7, 2, 10, 9 ])).toEqual(8)
})

test('with empty array', () => {
  expect(median([])).toBeNaN()
})

memoize

memoize<T, K extends any[]>(fn: (...inputs: K) => T): (...inputs: K) => T

When fn is called for a second time with the same input, then the cache result is returned instead of calling again fn.

let result = 0
const fn = (a,b) =>{
  result++

  return a + b
}
const memoized = R.memoize(fn)
memoized(1, 2)
memoized(1, 2)

// => `result` is equal to `1`

Try the above R.memoize example in Rambda REPL

All Typescript definitions
memoize<T, K extends any[]>(fn: (...inputs: K) => T): (...inputs: K) => T;
Tests
import { memoize } from './memoize'

test('memoize function without input arguments', () => {
  const fn = () => 4
  const memoized = memoize(fn)
  expect(typeof memoized()).toBe('function')
})

test('happy', () => {
  let counter = 0

  const fn = ({ a, b, c }) => {
    counter++

    return a + b - c
  }
  const memoized = memoize(fn)
  expect(memoized({
    a : 1,
    c : 3,
    b : 2,
  })).toBe(0)
  expect(counter).toBe(1)
  expect(memoized({
    c : 3,
    a : 1,
    b : 2,
  })).toBe(0)
  expect(counter).toBe(1)
})

test('normal function', () => {
  let counter = 0
  const fn = (a, b) => {
    counter++

    return a + b
  }
  const memoized = memoize(fn)
  expect(memoized(1, 2)).toBe(3)
  expect(memoized(1, 2)).toBe(3)
  expect(memoized(1, 2)).toBe(3)
  expect(counter).toBe(1)
  expect(memoized(2, 2)).toBe(4)
  expect(counter).toBe(2)
  expect(memoized(1, 2)).toBe(3)
  expect(counter).toBe(2)
})

test('async function', async () => {
  let counter = 0
  const delay = ms =>
    new Promise(resolve => {
      setTimeout(resolve, ms)
    })
  const fn = async (ms, a, b) => {
    await delay(ms)
    counter++

    return a + b
  }

  const memoized = memoize(fn)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(counter).toBe(1)
  expect(await memoized(
    100, 2, 2
  )).toBe(4)
  expect(counter).toBe(2)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(counter).toBe(2)
})

test('string as argument', () => {
  let count = 0
  const foo = 'foo'
  const tester = memoize(n => {
    count++

    return `${ n }bar`
  })
  tester(foo)
  tester(foo)
  tester(foo)

  expect(tester(foo)).toEqual('foobar')

  expect(count).toEqual(1)

  tester('baz')

  expect(tester('baz')).toEqual('bazbar')

  expect(count).toEqual(2)
})

merge

merge<O1 extends object, O2 extends object>(target: O1, newProps: O2): Merge<O2, O1, 'flat'>

It creates a copy of target object with overidden newProps properties.

const target = { 'foo': 0, 'bar': 1 }
const newProps = { 'foo': 7 }

const result = R.merge(target, newProps)
// => { 'foo': 7, 'bar': 1 }

Try the above R.merge example in Rambda REPL

All Typescript definitions
merge<O1 extends object, O2 extends object>(target: O1, newProps: O2): Merge<O2, O1, 'flat'>;
merge<O1 extends object>(target: O1): <O2 extends object>(newProps: O2) => Merge<O2, O1, 'flat'>;
Tests
import { merge } from './merge'

const obj = {
  foo : 1,
  bar : 2,
}

test('happy', () => {
  expect(merge(obj, { bar : 20 })).toEqual({
    foo : 1,
    bar : 20,
  })
})

test('curry', () => {
  expect(merge(obj)({ baz : 3 })).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

/**
 * https://github.com/selfrefactor/rambda/issues/77
 */
test('when undefined or null instead of object', () => {
  expect(merge(null, undefined)).toEqual({})
  expect(merge(obj, null)).toEqual(obj)
  expect(merge(obj, undefined)).toEqual(obj)
  expect(merge(undefined, obj)).toEqual(obj)
})

mergeAll

mergeAll<T>(list: object[]): T

It merges all objects of list array sequentially and returns the result.

const list = [
  {a: 1},
  {b: 2},
  {c: 3}
]
const result = R.mergeAll(list)
const expected = {
  a: 1,
  b: 2,
  c: 3
}
// => `result` is equal to `expected`

Try the above R.mergeAll example in Rambda REPL

All Typescript definitions
mergeAll<T>(list: object[]): T;
mergeAll(list: object[]): object;
Tests
import { mergeAll } from './mergeAll'

test('case 1', () => {
  const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]
  const expectedResult = {
    a : 1,
    b : 2,
    c : 3,
  }
  expect(mergeAll(arr)).toEqual(expectedResult)
})

test('case 2', () => {
  expect(mergeAll([ { foo : 1 }, { bar : 2 }, { baz : 3 } ])).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

mergeDeepRight

mergeDeepRight<O1 extends object, O2 extends object>(x: O1, y: O2): Merge<O2, O1, 'deep'>

Creates a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:

  • and both values are objects, the two values will be recursively merged
  • otherwise the value from the second object will be used.
All Typescript definitions
mergeDeepRight<O1 extends object, O2 extends object>(x: O1, y: O2): Merge<O2, O1, 'deep'>;
mergeDeepRight<O1 extends object>(x: O1): <O2 extends object>(y: O2) => Merge<O2, O1, 'deep'>;
Tests
// import { mergeDeepRight } from 'ramda'
import { mergeDeepRight } from './mergeDeepRight'

const slave = {
  name    : 'evilMe',
  age     : 10,
  contact : {
    a     : 1,
    email : 'foo@example.com',
  },
}
const master = {
  age     : 40,
  contact : { email : 'baz@example.com' },
  songs   : { title : 'Remains the same' },
}

test('happy', () => {
  const result = mergeDeepRight(slave, master)
  const curryResult = mergeDeepRight(slave)(master)
  const expected = {
    age     : 40,
    name    : 'evilMe',
    contact : {
      a     : 1,
      email : 'baz@example.com',
    },
    songs : { title : 'Remains the same' },
  }

  expect(result).toEqual(expected)
  expect(curryResult).toEqual(expected)
})

test('ramda compatible test 1', () => {
  const a = {
    w : 1,
    x : 2,
    y : { z : 3 },
  }
  const b = {
    a : 4,
    b : 5,
    c : { d : 6 },
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    w : 1,
    x : 2,
    y : { z : 3 },
    a : 4,
    b : 5,
    c : { d : 6 },
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 2', () => {
  const a = {
    a : {
      b : 1,
      c : 2,
    },
    y : 0,
  }
  const b = {
    a : {
      b : 3,
      d : 4,
    },
    z : 0,
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    a : {
      b : 3,
      c : 2,
      d : 4,
    },
    y : 0,
    z : 0,
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 3', () => {
  const a = {
    w : 1,
    x : { y : 2 },
  }
  const result = mergeDeepRight(a, { x : { y : 3 } })
  const expected = {
    w : 1,
    x : { y : 3 },
  }
  expect(result).toEqual(expected)
})

mergeLeft

mergeLeft<O1 extends object, O2 extends object>(target: O1, newProps: O2): Merge<O2, O1, 'flat'>

Same as R.merge, but in opposite direction.

const result = R.mergeLeft(
  {a: 10},
  {a: 1, b: 2}
)
// => {a:10, b: 2}

Try the above R.mergeLeft example in Rambda REPL

All Typescript definitions
mergeLeft<O1 extends object, O2 extends object>(target: O1, newProps: O2): Merge<O2, O1, 'flat'>;
mergeLeft<O1 extends object>(target: O1): <O2 extends object>(newProps: O2) => Merge<O2, O1, 'flat'>;
Tests
import { mergeLeft } from './mergeLeft'

const obj = {
  foo : 1,
  bar : 2,
}

test('happy', () => {
  expect(mergeLeft({ bar : 20 }, obj)).toEqual({
    foo : 1,
    bar : 20,
  })
})

test('curry', () => {
  expect(mergeLeft({ baz : 3 })(obj)).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

test('when undefined or null instead of object', () => {
  expect(mergeLeft(null, undefined)).toEqual({})
  expect(mergeLeft(obj, null)).toEqual(obj)
  expect(mergeLeft(obj, undefined)).toEqual(obj)
  expect(mergeLeft(undefined, obj)).toEqual(obj)
})

min

min<T extends Ord>(x: T, y: T): T

It returns the lesser value between x and y.

const result = [
  R.min(5, 7),  
  R.min('bar', 'foo'),  
]
// => [5, 'bar']

Try the above R.min example in Rambda REPL

All Typescript definitions
min<T extends Ord>(x: T, y: T): T;
min<T extends Ord>(x: T): (y: T) => T;
Tests
import { min } from './min'

test('happy', () => {
  expect(min(2, 1)).toBe(1)
  expect(min(2)(1)).toBe(1)
})

minBy

minBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T

It returns the lesser value between x and y according to compareFn function.

const compareFn = Math.abs

R.minBy(compareFn, -5, 2) // => -5

Try the above R.minBy example in Rambda REPL

All Typescript definitions
minBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T;
minBy<T>(compareFn: (input: T) => Ord, x: T): (y: T) => T;
minBy<T>(compareFn: (input: T) => Ord): FunctionToolbelt.Curry<(x: T, y: T) => T>;
Tests
import { minBy } from './minBy'

test('happy', () => {
  expect(minBy(
    Math.abs, -5, 2
  )).toEqual(2)
})

test('curried', () => {
  expect(minBy(Math.abs)(2, -5)).toEqual(2)
  expect(minBy(Math.abs)(2)(-5)).toEqual(2)
})

modulo

modulo(x: number, y: number): number

Curried version of x%y.

R.modulo(17, 3) // => 2

Try the above R.modulo example in Rambda REPL

All Typescript definitions
modulo(x: number, y: number): number;
modulo(x: number): (y: number) => number;
Tests
import { modulo } from './modulo'

test('happy', () => {
  expect(modulo(17, 3)).toEqual(2)
  expect(modulo(15)(6)).toEqual(3)
})

multiply

multiply(x: number, y: number): number

Curried version of x*y.

R.multiply(2, 4) // => 8

Try the above R.multiply example in Rambda REPL

All Typescript definitions
multiply(x: number, y: number): number;
multiply(x: number): (y: number) => number;
Tests
import { multiply } from './multiply'

test('happy', () => {
  expect(multiply(2, 4)).toEqual(8)
  expect(multiply(2)(4)).toEqual(8)
})

negate

negate(x: number): number
R.negate(420)// => -420

Try the above R.negate example in Rambda REPL

All Typescript definitions
negate(x: number): number;
Tests
import { negate } from './negate'

test('negate', () => {
  expect(negate(420)).toEqual(-420)
  expect(negate(-13)).toEqual(13)
})

nextIndex

nextIndex(index: number, list: any[]): number

It returns the next index of the list.

If we have reached the end of the list, then it will return 0.

const list = [1, 2, 3]

const result = [
  R.nextIndex(0, list),
  R.nextIndex(1, list),
  R.nextIndex(2, list),
  R.nextIndex(10, list)
]
// => [1, 2, 0, 0]

Try the above R.nextIndex example in Rambda REPL

All Typescript definitions
nextIndex(index: number, list: any[]): number;
Tests
import { nextIndex } from './nextIndex'

const list = [ 1, 2, 3, 4 ]

test('happy path', () => {
  expect(nextIndex(2, list)).toEqual(3)
})

test('go back to the start', () => {
  expect(nextIndex(3, list)).toEqual(0)
})

test('current index is too big', () => {
  expect(nextIndex(32, list)).toEqual(0)
})

none

none<T>(predicate: (x: T, index: number) => boolean, list: ReadonlyArray<T>): boolean

It returns true, if all members of array list returns false, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > 6

const result = R.none(predicate, arr)
// => true

Try the above R.none example in Rambda REPL

All Typescript definitions
none<T>(predicate: (x: T, index: number) => boolean, list: ReadonlyArray<T>): boolean;
none<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean;
none<T>(predicate: (x: T, index: number) => boolean): (list: ReadonlyArray<T>) => boolean;
none<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => boolean;
Tests
import { none } from './none'

const isEven = n => n % 2 === 0
const isOdd = n => n % 2 === 1
const arr = [ 1, 3, 5, 7, 9, 11 ]

test('when true', () => {
  expect(none(isEven, arr)).toBeTrue()
})

test('when false curried', () => {
  expect(none(isOdd)(arr)).toBeFalse()
})

test('passes index to predicate', () => {
  none((x, i) => {
    expect(typeof x).toBe('number')
    expect(typeof i).toBe('number')
  })([ 1, 2, 3 ])
})

not

not(input: any): boolean

It returns a boolean negated version of input.

R.not(false) // true

Try the above R.not example in Rambda REPL

All Typescript definitions
not(input: any): boolean;
Tests
import { not } from './not'

test('not', () => {
  expect(not(false)).toEqual(true)
  expect(not(true)).toEqual(false)
  expect(not(0)).toEqual(true)
  expect(not(1)).toEqual(false)
})

nth

nth<T>(index: number, list: ReadonlyArray<T>): T | undefined

Curried version of list[index].

const list = [1, 2, 3]
const str = 'foo'

const result = [
  R.nth(2, list),
  R.nth(6, list),
  R.nth(0, str),
]
// => [3, undefined, 'f']

Try the above R.nth example in Rambda REPL

All Typescript definitions
nth<T>(index: number, list: ReadonlyArray<T>): T | undefined;	
nth(index: number): <T>(list: ReadonlyArray<T>) => T | undefined;
Tests
import { nth } from './nth'

test('happy', () => {
  expect(nth(2, [ 1, 2, 3, 4 ])).toEqual(3)
})

test('with curry', () => {
  expect(nth(2)([ 1, 2, 3, 4 ])).toEqual(3)
})

test('with string', () => {
  expect(nth(2)('foo')).toEqual('o')
})

test('with negative index', () => {
  expect(nth(-3)([ 1, 2, 3, 4 ])).toEqual(2)
})

ok

ok(...inputs: any[]): (...schemas: any[]) => void | never

It checks if inputs are following schemas specifications according to R.isValid.

If validation fails, it throws.

const result = R.ok(
  1,
  ['foo', 'bar']
)(
  Number,
  [String]
)
// => undefined

Try the above R.ok example in Rambda REPL

All Typescript definitions
ok(...inputs: any[]): (...schemas: any[]) => void | never;
Tests
import { ok, schemaToString } from './ok'

test('happy', () => {
  expect(() => {
    ok(
      1, 'foo', {}
    )(
      'number', 'string', 'object'
    )
  }).not.toThrow()
})

test('when validation fails', () => {
  const errorMessage = `Failed R.ok -
reason: {"input":{},"schema":"string"}
all inputs: [1,"foo",{}]
all schemas: ["number","string","string"]`

  expect(() =>
    ok(
      1, 'foo', {}
    )(
      'number', 'string', 'string'
    )).toThrowWithMessage(Error, errorMessage)
})

/*
  TODO
  What about
  {a: Function}
*/
test('schema in error message', () => {
  const result = schemaToString({
    _a : [ Number ],
    a  : Number,
    b  : x => x > 2,
    c  : [ 'foo', 'bar' ],
    d  : [ { a : String } ],
    e  : 'boolean',
    f  : Array,
    h  : Object,
  })

  expect(JSON.stringify(result)).toMatchInlineSnapshot('"{\\"_a\\":\\"Array\\",\\"a\\":\\"number\\",\\"b\\":\\"Function\\",\\"c\\":\\"Array\\",\\"d\\":\\"Array\\",\\"e\\":\\"String\\",\\"f\\":\\"array\\",\\"h\\":\\"object\\"}"')
})

test('error contains schema', () => {
  try {
    ok(
      1, 'foo', {}
    )(
      { a : Number }, String, String
    )
    expect(false).toBeTrue()
  } catch (e){
    expect(e.message.startsWith('Failed R.ok -')).toBeTruthy()
    expect(e).toBeInstanceOf(Error)
  }
})

test('when not throws with single schema', () => {
  expect(() => ok(
    1, 2, 3
  )('number')).not.toThrow()
})

test('when throws with single schema', () => {
  expect(() => ok(
    1, 2, '3'
  )('number')).toThrow()
})

test('when throws with single input', () => {
  expect(() => ok('3')('number')).toThrow()
})

omit

omit<T, K extends string>(propsToOmit: readonly K[], obj: T): Omit<T, K>

It returns a partial copy of an obj without propsToOmit properties.

const obj = {a: 1, b: 2, c: 3}
const propsToOmit = 'a,c,d'
const propsToOmitList = ['a', 'c', 'd']

const result = [
  R.omit(propsToOmit, obj), 
  R.omit(propsToOmitList, obj) 
]
// => [{b: 2}, {b: 2}]

Try the above R.omit example in Rambda REPL

All Typescript definitions
omit<T, K extends string>(propsToOmit: readonly K[], obj: T): Omit<T, K>;
omit<K extends string>(propsToOmit: readonly K[]): <T>(obj: T) => Omit<T, K>;
omit<T, U>(propsToOmit: string, obj: T): U;
omit<T, U>(propsToOmit: string): (obj: T) => U;
omit<T>(propsToOmit: string, obj: object): T;
omit<T>(propsToOmit: string): (obj: object) => T;
Tests
import { omit } from './omit'

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = omit('a,c', obj)
  const resultCurry = omit('a,c')(obj)
  const expectedResult = { b : 2 }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with null', () => {
  expect(omit('a,b', null)).toEqual(undefined)
})

test('doesn\'t work with number as property', () => {
  expect(omit([ 42 ], {
    a  : 1,
    42 : 2,
  })).toEqual({
    42 : 2,
    a  : 1,
  })
})

test('happy', () => {
  expect(omit([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ b : 'bar' })
})

once

once<T extends (...args: any[]) => any>(func: T): T

It returns a function, which invokes only once fn function.

let result = 0
const addOnce = R.once((x) => result = result + x)

addOnce(1)
addOnce(1)
// => 1

Try the above R.once example in Rambda REPL

All Typescript definitions
once<T extends (...args: any[]) => any>(func: T): T;
Tests
import { once } from './once'

test('with counter', () => {
  let counter = 0
  const runOnce = once(x => {
    counter++

    return x + 2
  })
  expect(runOnce(1)).toEqual(3)
  runOnce(1)
  runOnce(1)
  runOnce(1)
  expect(counter).toEqual(1)
})

test('happy path', () => {
  const addOneOnce = once((
    a, b, c
  ) => a + b + c, 1)

  expect(addOneOnce(
    10, 20, 30
  )).toBe(60)
  expect(addOneOnce(40)).toEqual(60)
})

over

over<T>(lens: Lens, fn: Arity1Fn, value: T): T

It returns a copied Object or Array with modified value received by applying function fn to lens focus.

const headLens = R.lensIndex(0)
 
R.over(headLens, R.toUpper, ['foo', 'bar', 'baz']) //=> ['FOO', 'bar', 'baz']

Try the above R.over example in Rambda REPL

All Typescript definitions
over<T>(lens: Lens, fn: Arity1Fn, value: T): T;
over<T>(lens: Lens, fn: Arity1Fn, value: readonly T[]): T[];
over(lens: Lens, fn: Arity1Fn): <T>(value: T) => T;
over(lens: Lens, fn: Arity1Fn): <T>(value: readonly T[]) => T[];
over(lens: Lens): <T>(fn: Arity1Fn, value: T) => T;
over(lens: Lens): <T>(fn: Arity1Fn, value: readonly T[]) => T[];

partial

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T
All Typescript definitions
partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0, V1]): (x2: V2) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0]): (x1: V1, x2: V2) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0, V1, V2]): (x2: V3) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0, V1]): (x2: V2, x3: V3) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0]): (x1: V1, x2: V2, x3: V3) => T;
partial<T>(fn: (...a: readonly any[]) => T, args: readonly any[]): (...a: readonly any[]) => T;

partialCurry

partialCurry<Input, PartialInput, Output>(
  fn: (input: Input) => Output, 
  partialInput: PartialInput,
): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output

R.partialCurry is a curry helper designed specifically for functions accepting object as a single argument.

Initially the function knows only a part from the whole input object and then R.partialCurry helps in preparing the function for the second part, when it receives the rest of the input.

const fn = ({ a, b, c }) => a + b + c
const curried = partialCurry(fn, { a : 1 })
const result = curried({
  b : 2,
  c : 3,
})
// => 6

Try the above R.partialCurry example in Rambda REPL

All Typescript definitions
partialCurry<Input, PartialInput, Output>(
  fn: (input: Input) => Output, 
  partialInput: PartialInput,
): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output;
Tests
import { delay } from './delay'
import { partialCurry } from './partialCurry'
import { type } from './type'

test('with plain function', () => {
  const fn = ({ a, b, c }) => a + b + c
  const curried = partialCurry(fn, { a : 1 })

  expect(type(curried)).toEqual('Function')
  expect(curried({
    b : 2,
    c : 3,
  })).toEqual(6)
})

test('with function that throws an error', () => {
  const fn = ({ a, b, c }) => {
    throw new Error('foo')
  }
  const curried = partialCurry(fn, { a : 1 })

  expect(type(curried)).toEqual('Function')
  expect(() =>
    curried({
      b : 2,
      c : 3,
    })).toThrowWithMessage(Error, 'foo')
})

test('with async', async () => {
  const fn = async ({ a, b, c }) => {
    await delay(100)

    return a + b + c
  }

  const curried = partialCurry(fn, { a : 1 })

  const result = await curried({
    b : 2,
    c : 3,
  })

  expect(result).toEqual(6)
})

test('async function throwing an error', async () => {
  const fn = async ({ a, b, c }) => {
    await delay(100)
    throw new Error('foo')
  }

  const curried = partialCurry(fn, { a : 1 })

  try {
    await curried({
      b : 2,
      c : 3,
    })
    expect(true).toBeFalsy()
  } catch (e){
    expect(e.message).toBe('foo')
  }
})

partition

partition<T>(
  predicate: Predicatex<T>,
  input: T[]
): [T[], T[]]

It will return array of two objects/arrays according to predicate function. The first member holds all instanses of input that pass the predicate function, while the second member - those who doesn't.

input can be either an object or an array unlike Ramda where only array is a valid input.

const list = [1, 2, 3]
const obj = {a: 1, b: 2, c: 3}
const predicate = x => x > 2

const result = [
  R.partition(predicate, list),
  R.partition(predicate, obj)
]
const expected = [
  [[3], [1, 2]],
  [{c: 3},  {a: 1, b: 2}],
]
// `result` is equal to `expected`

Try the above R.partition example in Rambda REPL

All Typescript definitions
partition<T>(
  predicate: Predicatex<T>,
  input: T[]
): [T[], T[]];
partition<T>(
  predicate: Predicatex<T>
): (input: T[]) => [T[], T[]];
partition<T>(
  predicate: (x: T, prop?: string) => boolean,
  input: { [key: string]: T}
): [{ [key: string]: T}, { [key: string]: T}];
partition<T>(
  predicate: (x: T, prop?: string) => boolean
): (input: { [key: string]: T}) => [{ [key: string]: T}, { [key: string]: T}];
Tests
import { partition } from './partition'

test('with array', () => {
  const predicate = (x, i) => {
    expect(typeof i).toBe('number')

    return x > 2
  }
  const list = [ 1, 2, 3, 4 ]

  const result = partition(predicate, list)
  const expectedResult = [
    [ 3, 4 ],
    [ 1, 2 ],
  ]

  expect(result).toEqual(expectedResult)
})

test('with object', () => {
  const predicate = (value, prop) => {
    expect(typeof prop).toBe('string')

    return value > 2
  }
  const hash = {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  }

  const result = partition(predicate)(hash)
  const expectedResult = [
    {
      c : 3,
      d : 4,
    },
    {
      a : 1,
      b : 2,
    },
  ]

  expect(result).toEqual(expectedResult)
})

test('readme example', () => {
  const list = [ 1, 2, 3 ]
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const predicate = x => x > 2

  const result = [ partition(predicate, list), partition(predicate, obj) ]
  const expected = [
    [ [ 3 ], [ 1, 2 ] ],
    [
      { c : 3 },
      {
        a : 1,
        b : 2,
      },
    ],
  ]
  expect(result).toEqual(expected)
})

pass

pass(...inputs: any[]): (...rules: any[]) => boolean

It checks if inputs are following schemas specifications according to R.isValid.

const result = R.pass(
  1,
  ['foo','bar']
)(
  Number,
  [String]
)
// => true

Try the above R.pass example in Rambda REPL

All Typescript definitions
pass(...inputs: any[]): (...rules: any[]) => boolean;
Tests
import { pass } from './pass'

test('true on success', () => {
  const result = pass(
    1, 'foo', {}
  )(
    'number', 'string', 'object'
  )

  expect(result).toBeTrue()
})

test('false on failure', () => {
  expect(pass(
    1, 'foo', {}
  )(
    'number', 'string', 'string'
  )).toBeFalse()
})

test('true when single schema', () => {
  expect(pass(
    1, 2, 3
  )('number')).toBeTrue()
})

test('false when single schema', () => {
  expect(pass(
    1, 'foo', {}
  )('number')).toBeFalse()
})

test('array of schemas', () => {
  const result = pass([ { a : 1 }, { a : 2 }, { a : 3 } ])([ { a : Number } ])
  expect(result).toBeTruthy()
})

test('reame example', () => {
  const result = pass(1, [ 'foo', 'bar' ])(Number, [ String ])
  expect(result).toBeTruthy()
})

path

path<Input, T>(pathToSearch: string | string[], obj: Input): T | undefined

If pathToSearch is 'a.b' then it will return 1 if obj is {a:{b:1}}.

It will return undefined, if such path is not found.

const obj = {a: {b: 1}}
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const result = [
  R.path(pathToSearch, obj),
  R.path(pathToSearchList, obj),
  R.path('a.b.c.d', obj)
]
// => [1, 1, undefined]

Try the above R.path example in Rambda REPL

All Typescript definitions
path<Input, T>(pathToSearch: string | string[], obj: Input): T | undefined;
path<T>(pathToSearch: string | string[], obj: any): T | undefined;
path<T>(pathToSearch: string | string[]): (obj: any) => T | undefined;
path<Input, T>(pathToSearch: string | string[]): (obj: Input) => T | undefined;
Tests
import { path } from './path'

test('with array inside object', () => {
  const obj = { a : { b : [ 1, { c : 1 } ] } }

  expect(path('a.b.1.c', obj)).toBe(1)
})

test('works with undefined', () => {
  const obj = { a : { b : { c : 1 } } }

  expect(path('a.b.c.d.f', obj)).toBeUndefined()
  expect(path('foo.babaz', undefined)).toBeUndefined()
  expect(path('foo.babaz')(undefined)).toBeUndefined()
})

test('works with string instead of array', () => {
  expect(path('foo.bar.baz')({ foo : { bar : { baz : 'yes' } } })).toEqual('yes')
})

test('path', () => {
  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : { baz : 'yes' } } })).toEqual('yes')

  expect(path([ 'foo', 'bar', 'baz' ])(null)).toBeUndefined()

  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : 'baz' } })).toBeUndefined()
})

pathEq

pathEq(pathToSearch: Path, target: any, input: any): boolean

It returns true if pathToSearch of input object is equal to target value.

pathToSearch is passed to R.path, which means that it can be either a string or an array. Also equality between target and the found value is determined by R.equals.

const path = 'a.b'
const target = {c: 1}
const input = {a: {b: {c: 1}}}

const result = R.pathEq(
  path,
  target,
  input
)
// => true

Try the above R.pathEq example in Rambda REPL

All Typescript definitions
pathEq(pathToSearch: Path, target: any, input: any): boolean;
pathEq(pathToSearch: Path, target: any): (input: any) => boolean;
pathEq(pathToSearch: Path): FunctionToolbelt.Curry<(a: any, b: any) => boolean>;
Tests
import { pathEq } from './pathEq'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : { c : 1 } } }
  const target = { c : 1 }

  expect(pathEq(
    path, target, obj
  )).toBeTrue()
})

test('when false', () => {
  const path = 'a.b'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(path, target)(obj)).toBeFalse()
})

test('when wrong path', () => {
  const path = 'foo.bar'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(
    path, target, obj
  )).toBeFalse()
})

pathOr

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T

It reads obj input and returns either R.path(pathToSearch, obj) result or defaultValue input.

const defaultValue = 'DEFAULT_VALUE'
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const obj = {
  a : {
    b : 1
  }
}

const result = [
  R.pathOr(DEFAULT_VALUE, pathToSearch, obj) 
  R.pathOr(DEFAULT_VALUE, pathToSearchList, obj) 
  R.pathOr(DEFAULT_VALUE, 'a.b.c', obj) 
]
// => [1, 1, 'DEFAULT_VALUE']

Try the above R.pathOr example in Rambda REPL

All Typescript definitions
pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T;
pathOr<T>(defaultValue: T, pathToSearch: Path): (obj: any) => T;
pathOr<T>(defaultValue: T): FunctionToolbelt.Curry<(a: Path, b: any) => T>;
Tests
import { pathOr } from './pathOr'

test('with undefined', () => {
  const result = pathOr(
    'foo', 'x.y', { x : { y : 1 } }
  )

  expect(result).toEqual(1)
})

test('with null', () => {
  const result = pathOr(
    'foo', 'x.y', null
  )

  expect(result).toEqual('foo')
})

test('with NaN', () => {
  const result = pathOr(
    'foo', 'x.y', NaN
  )

  expect(result).toEqual('foo')
})

test('curry case (x)(y)(z)', () => {
  const result = pathOr('foo')('x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toEqual('foo')
})

test('curry case (x)(y,z)', () => {
  const result = pathOr('foo', 'x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toEqual('foo')
})

test('curry case (x,y)(z)', () => {
  const result = pathOr('foo')('x.y.z', { x : { y : { a : 1 } } })

  expect(result).toEqual('foo')
})

paths

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[]

It loops over members of pathsToSearch as singlePath and returns the array produced by R.path(singlePath, obj).

Because it calls R.path, then singlePath can be either string or a list.

const obj = {
  a : {
    b : {
      c : 1,
      d : 2
    }
  }
}

const result = R.paths([
  'a.b.c',
  'a.b.c.d',
  'a.b.c.d.e',
], obj)
// => [1, 2, undefined]

Try the above R.paths example in Rambda REPL

All Typescript definitions
paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[];
paths<Input, T>(pathsToSearch: Path[]): (obj: Input) => (T | undefined)[];
paths<T>(pathsToSearch: Path[], obj: any): (T | undefined)[];
paths<T>(pathsToSearch: Path[]): (obj: any) => (T | undefined)[];
Tests
import { paths } from './paths'

const obj = {
  a : {
    b : {
      c : 1,
      d : 2,
    },
  },
  p : [ { q : 3 }, 'Hi' ],
  x : {
    y : 'Alice',
    z : [ [ {} ] ],
  },
}

test('with string path + curry', () => {
  const pathsInput = [ 'a.b.d', 'p.q' ]
  const expected = [ 2, undefined ]
  const result = paths(pathsInput, obj)
  const curriedResult = paths(pathsInput)(obj)

  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
})

test('with array path', () => {
  const result = paths([
    [ 'a', 'b', 'c' ],
    [ 'x', 'y' ],
  ],
  obj)

  expect(result).toEqual([ 1, 'Alice' ])
})

test('takes a paths that contains indices into arrays', () => {
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 0, 0 ],
  ],
  obj)).toEqual([ 3, {} ])
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 2, 1 ],
  ],
  obj)).toEqual([ 3, undefined ])
})

test('gets a deep property\'s value from objects', () => {
  expect(paths([ [ 'a', 'b' ] ], obj)).toEqual([ obj.a.b ])
  expect(paths([ [ 'p', 0 ] ], obj)).toEqual([ obj.p[ 0 ] ])
})

test('returns undefined for items not found', () => {
  expect(paths([ [ 'a', 'x', 'y' ] ], obj)).toEqual([ undefined ])
  expect(paths([ [ 'p', 2 ] ], obj)).toEqual([ undefined ])
})

pick

pick<T, K extends string | number | symbol>(propsToPick: readonly K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>

It returns a partial copy of an input containing only propsToPick properties.

input can be either an object or an array.

String anotation of propsToPick is one of the differences between Rambda and Ramda.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const list = [1, 2, 3, 4]
const propsToPick = 'a,foo'
const propsToPickList = ['a', 'foo']

const result = [
  R.pick(propsToPick, obj),
  R.pick(propsToPickList, obj),
  R.pick('a,bar', obj),
  R.pick('bar', obj),
  R.pick([0, 3], list),
  R.pick('0,3', list),
]

const expected = [
  {a:1, foo: 'cherry'},
  {a:1, foo: 'cherry'},
  {a:1},
  {},
  [1,4],
  [1,4]
]
// => `result` is equal to `expected`

Try the above R.pick example in Rambda REPL

All Typescript definitions
pick<T, K extends string | number | symbol>(propsToPick: readonly K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<K extends string | number | symbol>(propsToPick: readonly K[]): <T>(input: T) => Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<T, U>(propsToPick: string, input: T): U;
pick<T, U>(propsToPick: string): (input: T) => U;
pick<T>(propsToPick: string, input: object): T;
pick<T>(propsToPick: string): (input: object) => T;
Tests
import { pick } from './pick'

const obj = {
  a : 1,
  b : 2,
  c : 3,
}

test('props to pick is a string', () => {
  const result = pick('a,c', obj)
  const resultCurry = pick('a,c')(obj)
  const expectedResult = {
    a : 1,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('when prop is missing', () => {
  const result = pick('a,d,f', obj)
  expect(result).toEqual({ a : 1 })
})

test('props to pick is an array', () => {
  expect(pick([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    c : 'baz',
  })

  expect(pick([ 'a', 'd', 'e', 'f' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ a : 'foo' })

  expect(pick('a,d,e,f')(null)).toEqual(undefined)
})

test('works with list as input and number as props - props to pick is an array', () => {
  const result = pick([ 1, 2 ], [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('works with list as input and number as props - props to pick is a string', () => {
  const result = pick('1,2', [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('with symbol', () => {
  const symbolProp = Symbol('s')
  expect(pick([ symbolProp ], { [ symbolProp ] : 'a' })).toMatchInlineSnapshot(`
    Object {
      Symbol(s): "a",
    }
  `)
})

pickAll

pickAll<T, U>(propsToPick: readonly string[], input: T): U

Same as R.pick but it won't skip the missing props, i.e. it will assign them to undefined.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const propsToPick = 'a,foo,bar'
const propsToPickList = ['a', 'foo', 'bar']

const result = [
  R.pickAll(propsToPick, obj),
  R.pickAll(propsToPickList, obj),
  R.pickAll('a,bar', obj),
  R.pickAll('bar', obj),
]
const expected = [
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, bar: undefined},
  {bar: undefined}
]
// => `result` is equal to `expected`

Try the above R.pickAll example in Rambda REPL

All Typescript definitions
pickAll<T, U>(propsToPick: readonly string[], input: T): U;
pickAll<T, U>(propsToPick: readonly string[]): (input: T) => U;
pickAll<T, U>(propsToPick: string, input: T): U;
pickAll<T, U>(propsToPick: string): (input: T) => U;
Tests
import { pickAll } from './pickAll'

test('when input is undefined or null', () => {
  expect(pickAll('a', null)).toBe(undefined)
  expect(pickAll('a', undefined)).toBe(undefined)
})

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = pickAll('a,c', obj)
  const resultCurry = pickAll('a,c')(obj)
  const expectedResult = {
    a : 1,
    b : undefined,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with array as condition', () => {
  expect(pickAll([ 'a', 'b', 'c' ], {
    a : 'foo',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    b : undefined,
    c : 'baz',
  })
})

pipe

pipe<T1>(fn0: () => T1): () => T1

It performs left-to-right function composition.

const result = R.pipe(
  R.filter(val => val > 2),
  R.map(a => a * 2)
)([1, 2, 3, 4])

// => [6, 8]

Try the above R.pipe example in Rambda REPL

All Typescript definitions
pipe<T1>(fn0: () => T1): () => T1;
pipe<V0, T1>(fn0: (x0: V0) => T1): (x0: V0) => T1;
pipe<V0, V1, T1>(fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T1;
pipe<V0, V1, V2, T1>(fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T1;

pipe<T1, T2>(fn0: () => T1, fn1: (x: T1) => T2): () => T2;
pipe<V0, T1, T2>(fn0: (x0: V0) => T1, fn1: (x: T1) => T2): (x0: V0) => T2;
pipe<V0, V1, T1, T2>(fn0: (x0: V0, x1: V1) => T1, fn1: (x: T1) => T2): (x0: V0, x1: V1) => T2;
pipe<V0, V1, V2, T1, T2>(fn0: (x0: V0, x1: V1, x2: V2) => T1, fn1: (x: T1) => T2): (x0: V0, x1: V1, x2: V2) => T2;

pipe<T1, T2, T3>(fn0: () => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3): () => T3;
pipe<V0, T1, T2, T3>(fn0: (x: V0) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3): (x: V0) => T3;
pipe<V0, V1, T1, T2, T3>(fn0: (x0: V0, x1: V1) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3): (x0: V0, x1: V1) => T3;
pipe<V0, V1, V2, T1, T2, T3>(fn0: (x0: V0, x1: V1, x2: V2) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3): (x0: V0, x1: V1, x2: V2) => T3;

pipe<T1, T2, T3, T4>(fn0: () => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4): () => T4;
pipe<V0, T1, T2, T3, T4>(fn0: (x: V0) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4): (x: V0) => T4;
pipe<V0, V1, T1, T2, T3, T4>(fn0: (x0: V0, x1: V1) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4): (x0: V0, x1: V1) => T4;
pipe<V0, V1, V2, T1, T2, T3, T4>(fn0: (x0: V0, x1: V1, x2: V2) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4): (x0: V0, x1: V1, x2: V2) => T4;

pipe<T1, T2, T3, T4, T5>(fn0: () => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4, fn4: (x: T4) => T5): () => T5;
pipe<V0, T1, T2, T3, T4, T5>(fn0: (x: V0) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4, fn4: (x: T4) => T5): (x: V0) => T5;
pipe<V0, V1, T1, T2, T3, T4, T5>(fn0: (x0: V0, x1: V1) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4, fn4: (x: T4) => T5): (x0: V0, x1: V1) => T5;
pipe<V0, V1, V2, T1, T2, T3, T4, T5>(fn0: (x0: V0, x1: V1, x2: V2) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4, fn4: (x: T4) => T5): (x0: V0, x1: V1, x2: V2) => T5;

pipe<T1, T2, T3, T4, T5, T6>(fn0: () => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4, fn4: (x: T4) => T5, fn5: (x: T5) => T6): () => T6;
pipe<V0, T1, T2, T3, T4, T5, T6>(fn0: (x: V0) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4, fn4: (x: T4) => T5, fn5: (x: T5) => T6): (x: V0) => T6;
pipe<V0, V1, T1, T2, T3, T4, T5, T6>(fn0: (x0: V0, x1: V1) => T1, fn1: (x: T1) => T2, fn2: (x: T2) => T3, fn3: (x: T3) => T4, fn4: (x: T4) => T5, fn5: (x: T5) => T6): (x0: V0, x1: V1) => T6;
pipe<V0, V1, V2, T1, T2, T3, T4, T5, T6>(
  fn0: (x0: V0, x1: V1, x2: V2) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6): (x0: V0, x1: V1, x2: V2) => T6;

pipe<T1, T2, T3, T4, T5, T6, T7>(
  fn0: () => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn: (x: T6) => T7): () => T7;
pipe<V0, T1, T2, T3, T4, T5, T6, T7>(
  fn0: (x: V0) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn: (x: T6) => T7): (x: V0) => T7;
pipe<V0, V1, T1, T2, T3, T4, T5, T6, T7>(
  fn0: (x0: V0, x1: V1) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7): (x0: V0, x1: V1) => T7;
pipe<V0, V1, V2, T1, T2, T3, T4, T5, T6, T7>(
  fn0: (x0: V0, x1: V1, x2: V2) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7): (x0: V0, x1: V1, x2: V2) => T7;

pipe<T1, T2, T3, T4, T5, T6, T7, T8>(
  fn0: () => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn: (x: T7) => T8): () => T8;
pipe<V0, T1, T2, T3, T4, T5, T6, T7, T8>(
  fn0: (x: V0) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn: (x: T7) => T8): (x: V0) => T8;
pipe<V0, V1, T1, T2, T3, T4, T5, T6, T7, T8>(
  fn0: (x0: V0, x1: V1) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8): (x0: V0, x1: V1) => T8;
pipe<V0, V1, V2, T1, T2, T3, T4, T5, T6, T7, T8>(
  fn0: (x0: V0, x1: V1, x2: V2) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8): (x0: V0, x1: V1, x2: V2) => T8;

pipe<T1, T2, T3, T4, T5, T6, T7, T8, T9>(
  fn0: () => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9): () => T9;
pipe<V0, T1, T2, T3, T4, T5, T6, T7, T8, T9>(
  fn0: (x0: V0) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9): (x0: V0) => T9;
pipe<V0, V1, T1, T2, T3, T4, T5, T6, T7, T8, T9>(
  fn0: (x0: V0, x1: V1) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9): (x0: V0, x1: V1) => T9;
pipe<V0, V1, V2, T1, T2, T3, T4, T5, T6, T7, T8, T9>(
  fn0: (x0: V0, x1: V1, x2: V2) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9): (x0: V0, x1: V1, x2: V2) => T9;

pipe<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
  fn0: () => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9,
  fn9: (x: T9) => T10): () => T10;
pipe<V0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
  fn0: (x0: V0) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9,
  fn9: (x: T9) => T10): (x0: V0) => T10;
pipe<V0, V1, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
  fn0: (x0: V0, x1: V1) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9,
  fn9: (x: T9) => T10): (x0: V0, x1: V1) => T10;
pipe<V0, V1, V2, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
  fn0: (x0: V0, x1: V1, x2: V2) => T1,
  fn1: (x: T1) => T2,
  fn2: (x: T2) => T3,
  fn3: (x: T3) => T4,
  fn4: (x: T4) => T5,
  fn5: (x: T5) => T6,
  fn6: (x: T6) => T7,
  fn7: (x: T7) => T8,
  fn8: (x: T8) => T9,
  fn9: (x: T9) => T10): (x0: V0, x1: V1, x2: V2) => T10;
Tests
import { add, last, map } from '../rambda'
import { pipe } from './pipe'

test('happy', () => {
  const list = [ 1, 2, 3 ]

  const result = pipe(
    map(add(1)), map(add(10)), last
  )(list)

  expect(result).toEqual(14)
})

test('with bad input', () => {
  expect(() => pipe()).toThrowWithMessage(Error,
    'pipe requires at least one argument')
})

piped

piped<T>(input: any, ...fnList: Func<any>[]): T

It is basically R.pipe, but instead of passing input argument as R.pipe(...)(input), you pass it as the first argument.

const result = piped(
  [1, 2, 3],
  R.filter(x => x > 1),
  R.map(x => x*10),
)
// => [20, 30]

Try the above R.piped example in Rambda REPL

All Typescript definitions
piped<T>(input: any, ...fnList: Func<any>[]): T;
Tests
import { add } from './add'
import { filter } from './filter'
import { map } from './map'
import { piped } from './piped'

test('happy', () => {
  const result = piped(
    [ 1, 2, 3 ],
    filter(x => x > 1),
    map(x => x * 10),
    map(add(1))
  )
  const expectedResult = [ 21, 31 ]

  expect(result).toEqual(expectedResult)
})

pipedAsync

pipedAsync<T>(
  input: any,
  ...fns: (Func<any> | Async<any>)[]
): Promise<T>
All Typescript definitions
pipedAsync<T>(
  input: any,
  ...fns: (Func<any> | Async<any>)[]
): Promise<T>;

pluck

pluck<T>(property: number, list: ReadonlyArray<T>): T

It returns list of the values of property taken from the all objects inside list.

const list = [{a: 1}, {a: 2}, {b: 3}]
const property = 'a'

R.pluck(list, property) 
// => [1, 2]

Try the above R.pluck example in Rambda REPL

All Typescript definitions
pluck<T>(property: number, list: ReadonlyArray<T>): T;
pluck<K extends keyof T, T>(property: K, list: ReadonlyArray<T>): T[K][];
pluck(property: number): <T>(list: ReadonlyArray<T>) => T;
pluck<P extends string>(property: P): <T>(list: ReadonlyArray<Record<P, T>>) => T[];
Tests
import { pluck } from './pluck'

test('happy', () => {
  expect(pluck('a')([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ 1, 2 ])
})

test('with number', () => {
  const input = [
    [ 1, 2 ],
    [ 3, 4 ],
  ]

  expect(pluck(0, input)).toEqual([ 1, 3 ])
})

prepend

prepend<T>(x: T, listOrString: ReadonlyArray<T>): T[]

It adds element x at the beginning of listOrString.

const x = 'foo'

const result = [
  R.prepend(x, '_cherry'),
  R.prepend(x, ['bar', 'baz'])
]
// => ['foo_cherry', ['foo', 'bar', 'baz']]

Try the above R.prepend example in Rambda REPL

All Typescript definitions
prepend<T>(x: T, listOrString: ReadonlyArray<T>): T[];
prepend<T>(x: T): (listOrString: ReadonlyArray<T>) => T[];
Tests
import { prepend } from './prepend'

test('happy', () => {
  expect(prepend('f', 'oo')).toEqual('foo')
})

test('prepend', () => {
  expect(prepend('yes', [ 'foo', 'bar', 'baz' ])).toEqual([
    'yes',
    'foo',
    'bar',
    'baz',
  ])

  expect(prepend('foo')([])).toEqual([ 'foo' ])
})

prevIndex

prevIndex(index: number, list: any[]): number

It returns the next index of the list when the order is descending.

If we have reached the beginning of the list, then it will return the last index of the list.

const list = [1, 2, 3]

const result = [
  R.prevIndex(0, list),
  R.prevIndex(1, list),
  R.prevIndex(2, list),
]
// => [2, 0, 1]

Try the above R.prevIndex example in Rambda REPL

All Typescript definitions
prevIndex(index: number, list: any[]): number;
Tests
import { prevIndex } from './prevIndex'

const list = [ 1, 2, 3, 4 ]

test('happy path 1', () => {
  expect(prevIndex(2, list)).toEqual(1)
})

test('happy path 2', () => {
  expect(prevIndex(0, list)).toEqual(3)
})

produce

produce<Input, Output>(
  rules: ProduceRules<Input>,
  input: Input
): Output

It returns an object created by applying each value of rules to input argument

rules input is an object with synchronous or asynchronous functions as values.

If there is at least one member of rules that is asynchronous, then the return value is a promise.

const rules = {
  foo: x =>  > 10,
  bar: x => ({baz: x})
}
const input = 7
const result = R.produce(rules, input)

const expected = {
  foo: false,
  bar: {baz: 7}
}
// => `result` is equal to `expected`

Try the above R.produce example in Rambda REPL

All Typescript definitions
produce<Input, Output>(
  rules: ProduceRules<Input>,
  input: Input
): Output;
produce<Input, Output>(
  rules: ProduceRules<Input>
): (
  input: Input
) => Output;
Tests
import { delay } from './delay'
import { produce } from './produce'

test('async', async () => {
  const fn = produce({
    foo : async x => {
      await delay(100)

      return `${ x }_ZEPPELIN`
    },
    bar : inputArgument => inputArgument === 5,
  })
  const expected = {
    foo : 'LED_ZEPPELIN',
    bar : false,
  }

  const result = await fn('LED')
  expect(result).toEqual(expected)
})

test('async with error', async () => {
  const fn = produce({
    foo : async x => {
      await delay(100)
      throw new Error(`${ x }_ZEPPELIN`)
    },
    bar : inputArgument => inputArgument === 5,
  })

  try {
    await fn('LED')
    expect(1).toBe(2)
  } catch (e){
    expect(e.message).toBe('LED_ZEPPELIN')
  }
})

test('sync', () => {
  const fn = produce({
    foo : x => x + 1,
    bar : inputArgument => inputArgument === 5,
  })
  const expected = {
    foo : 6,
    bar : true,
  }

  const result = fn(5)
  expect(result).toEqual(expected)
})

product

product(list: ReadonlyArray<number>): number
R.product([ 2, 3, 4 ])
// => 24)

Try the above R.product example in Rambda REPL

All Typescript definitions
product(list: ReadonlyArray<number>): number;
Tests
import { product } from './product'

test('happy', () => {
  expect(product([ 2, 3, 4 ])).toEqual(24)
})

test('bad input', () => {
  expect(product([ null ])).toEqual(0)
  expect(product([])).toEqual(1)
})

prop

prop<P extends keyof T, T>(propToFind: P, obj: T): T[P]

It returns the value of property propToFind in obj.

If there is no such property, it returns undefined.

const result = [
  R.prop('x', {x: 100}), 
  R.prop('x', {a: 1}) 
]
// => [100, undefined]

Try the above R.prop example in Rambda REPL

All Typescript definitions
prop<P extends keyof T, T>(propToFind: P, obj: T): T[P];
prop<P extends string>(p: P): <T>(propToFind: Record<P, T>) => T;
prop<P extends string, T>(p: P): (propToFind: Record<P, T>) => T;
Tests
import { prop } from './prop'

test('prop', () => {
  expect(prop('foo')({ foo : 'baz' })).toEqual('baz')

  expect(prop('bar')({ foo : 'baz' })).toEqual(undefined)

  expect(prop('bar')(null)).toEqual(undefined)
})

propEq

propEq<T, K extends keyof T>(propToFind: K, valueToMatch: T[K], obj: T): boolean

It returns true if obj has property propToFind and its value is equal to valueToMatch.

const obj = { foo: 'bar' }
const secondObj = { foo: 1 }

const propToFind = 'foo'
const valueToMatch = 'bar'

const result = [
  R.propEq(propToFind, valueToMatch, obj),
  R.propEq(propToFind, valueToMatch, secondObj)
]
// => [true, false]

Try the above R.propEq example in Rambda REPL

All Typescript definitions
propEq<T, K extends keyof T>(propToFind: K, valueToMatch: T[K], obj: T): boolean;
propEq<T, K extends keyof T>(propToFind: K, valueToMatch: T[K]): (obj: T) => boolean;
propEq<T, K extends keyof T>(propToFind: K): {
   (valueToMatch: T[K], obj: T): boolean;
   (valueToMatch: T[K]): (obj: T) => boolean;
};
Tests
import { propEq } from './propEq'

test('happy', () => {
  expect(propEq('foo', 'bar')({ foo : 'bar' })).toBeTrue()
  expect(propEq('foo', 'bar')({ foo : 'baz' })).toBeFalse()
  expect(propEq('foo')('bar')({ foo : 'baz' })).toBeFalse()
  expect(propEq(
    'foo', 'bar', null
  )).toBeFalse()
})

propIs

propIs(type: any, name: string, obj: any): boolean

It returns true if property of obj is from target type.

const obj = {a:1, b: 'foo'}
const property = 'foo'

const result = [
  R.propIs(String, property, obj),
  R.propIs(Number, property, obj)
]
// => [true, false]

Try the above R.propIs example in Rambda REPL

All Typescript definitions
propIs(type: any, name: string, obj: any): boolean;
propIs(type: any, name: string): (obj: any) => boolean;
propIs(type: any): {
    (name: string, obj: any): boolean;
    (name: string): (obj: any) => boolean;
};
Tests
import { propIs } from './propIs'

const obj = { value : 1 }
const property = 'value'

test('when true', () => {
  expect(propIs(
    Number, property, obj
  )).toBeTrue()
})

test('when false', () => {
  expect(propIs(
    String, property, obj
  )).toBeFalse()
  expect(propIs(
    String, property, {}
  )).toBeFalse()
})

propOr

propOr<T>(defaultValue: T, property: string, obj: { [key: string]: T}): T

It returns either defaultValue or the value of property in obj.

const obj = {a: 1}
const defaultValue = 'DEFAULT_VALUE'
const property = 'a'

const result = [
  R.propOr(defaultValue, property, obj),
  R.propOr(defaultValue, 'foo', obj)
]
// => [1, 'DEFAULT_VALUE']

Try the above R.propOr example in Rambda REPL

All Typescript definitions
propOr<T>(defaultValue: T, property: string, obj: { [key: string]: T}): T;
propOr<T>(defaultValue: T, property: string): (obj: { [key: string]: T}) => T;
propOr<T>(defaultValue: T): FunctionToolbelt.Curry<(property: string, obj: { [key: string]: T}) => T>;
Tests
import { propOr } from './propOr'

test('propOr (result)', () => {
  const obj = { a : 1 }
  expect(propOr(
    'default', 'a', obj
  )).toEqual(1)
  expect(propOr(
    'default', 'notExist', obj
  )).toEqual('default')
  expect(propOr(
    'default', 'notExist', null
  )).toEqual('default')
})

test('propOr (currying)', () => {
  const obj = { a : 1 }
  expect(propOr('default')('a', obj)).toEqual(1)
  expect(propOr('default', 'a')(obj)).toEqual(1)
  expect(propOr('default')('notExist', obj)).toEqual('default')
  expect(propOr('default', 'notExist')(obj)).toEqual('default')
})

random

random(minInclusive: number, maxInclusive: number): number

It returns a random number between min inclusive and max inclusive.

All Typescript definitions
random(minInclusive: number, maxInclusive: number): number;
Tests
import { random } from './random'
import { range } from './range'

test('when returns true', () => {
  range(0, 100).map(() => {
    const randomResult = random(1, 10)
    expect(randomResult).toBeLessThanOrEqual(10)
    expect(randomResult).toBeGreaterThanOrEqual(1)
  })
})

range

range(start: number, end: number): number[]

It returns list of numbers between start(inclusive) to end(exclusive) numbers.

R.range(0, 5)
// => [0, 1, 2, 3, 4]

Try the above R.range example in Rambda REPL

All Typescript definitions
range(start: number, end: number): number[];
range(start: number): (end: number) => number[];
Tests
import { range } from './range'

test('happy', () => {
  expect(range(0, 10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

test('end range is bigger than start range', () => {
  expect(range(7, 3)).toEqual([])
  expect(range(5, 5)).toEqual([])
})

test('with bad input', () => {
  const throwMessage = 'Both arguments to range must be numbers'
  expect(() => range('a', 6)).toThrowWithMessage(Error, throwMessage)
  expect(() => range(6, 'z')).toThrowWithMessage(Error, throwMessage)
})

test('curry', () => {
  expect(range(0)(10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

reduce

reduce<T, TResult>(reducer: (prev: TResult, current: T, i: number) => TResult, initialValue: TResult, list: ReadonlyArray<T>): TResult
const list = [1, 2, 3]
const initialValue = 10
const reducer = (prev, current) => prev * current

const result = R.reduce(reducer, initialValue, list)
// => 60

Try the above R.reduce example in Rambda REPL

All Typescript definitions
reduce<T, TResult>(reducer: (prev: TResult, current: T, i: number) => TResult, initialValue: TResult, list: ReadonlyArray<T>): TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T) => TResult, initialValue: TResult, list: ReadonlyArray<T>): TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T, i?: number) => TResult): (initialValue: TResult, list: ReadonlyArray<T>) => TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T, i?: number) => TResult, initialValue: TResult): (list: ReadonlyArray<T>) => TResult;
Tests
import { reduce } from './reduce'

const reducer = (
  prev, current, i
) => {
  expect(i).toBeNumber()

  return prev + current
}
const initialValue = 1
const list = [ 1, 2, 3 ]

test('happy', () => {
  expect(reduce(
    reducer, initialValue, list
  )).toEqual(7)
})

test('with object as iterable', () => {
  expect(() =>
    reduce(
      reducer, initialValue, {
        a : 1,
        b : 2,
      }
    )).toThrowWithMessage(TypeError, 'reduce: list must be array or iterable')
})

test('with undefined as iterable', () => {
  expect(() => reduce(
    reducer, initialValue, undefined
  )).toThrowWithMessage(TypeError,
    'reduce: list must be array or iterable')
})

reject

reject<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[]

It has the opposite effect of R.filter.

It will return those members of list that return false when applied to predicate function.

const list = [1, 2, 3, 4]
const predicate = x => x > 2

const result = [
  R.reject(predicate, list)
]
// => [1, 2]

Try the above R.reject example in Rambda REPL

All Typescript definitions
reject<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[];
reject<T>(predicate: FilterFunctionArray<T>, x: T[]): T[];
reject<T, U>(predicate: FilterFunctionObject<T>): (x: Dictionary<T>) => Dictionary<T>;
reject<T>(predicate: FilterFunctionObject<T>, x: Dictionary<T>): Dictionary<T>;
Tests
import { reject } from './reject'

const isOdd = n => n % 2 === 1

test('with array', () => {
  expect(reject(isOdd, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
})

test('with object', () => {
  expect(reject(isOdd, {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  })).toEqual({
    b : 2,
    d : 4,
  })
})

test('pass index as second argument', () => {
  reject((x, i) => {
    expect(typeof x).toBe('number')
    expect(typeof i).toBe('number')
  },
  [ 10, 12, 15 ])
})

remove

remove(
  toRemove: string | RegExp | (string | RegExp)[],
  text: string
): string

It will remove all toRemove entries from text sequentially.

toRemove argument can be either a list of strings/regular expressions or a single string/regular expression.

const result = remove(
  ['foo','bar'],
  'foo bar baz foo'
)
// => 'baz foo'

Try the above R.remove example in Rambda REPL

All Typescript definitions
remove(
  toRemove: string | RegExp | (string | RegExp)[],
  text: string
): string;
remove(
  toRemove: string | RegExp | (string | RegExp)[]
): (text: string) => string;
Tests
import { remove } from './remove'

test('happy', () => {
  const inputs = [ /foo/, /not\shere/, /also/, 'bar' ]
  const text = 'foo bar baz foo'

  const result = remove(inputs)(text)
  const expectedResult = 'baz foo'

  expect(result).toEqual(expectedResult)
})

test('with strings + curry', () => {
  const inputs = [ 'foo', 'bar' ]
  const text = 'foo bar baz foo'

  const result = remove(inputs)(text)
  const expectedResult = 'baz foo'

  expect(result).toEqual(expectedResult)
})

test('with strings and regex', () => {
  const inputs = [ /foo/g, 'bar' ]
  const text = 'foo bar baz foo'

  const result = remove(inputs, text)
  const expectedResult = 'baz'

  expect(result).toEqual(expectedResult)
})

test('text is not string', () => {
  const inputs = [ /foo/g, 'bar' ]
  const text = null

  expect(() => remove(inputs, text)).toThrowWithMessage(Error,
    'R.remove requires string not Null')
})

test('with regexes', () => {
  const inputs = [ /foo/g, /bar/ ]
  const text = 'foo bar baz foo'

  const result = remove(inputs, text)
  const expectedResult = 'baz'

  expect(result).toEqual(expectedResult)
})

test('with single rule', () => {
  const inputs = /foo/g
  const text = 'foo bar baz foo'

  const result = remove(inputs, text)
  const expectedResult = 'bar baz'

  expect(result).toEqual(expectedResult)
})

renameProps

renameProps(rules: object, input: object): object

If property prop of rules is also a property in input, then rename input property to rules[prop].

All Typescript definitions
renameProps(rules: object, input: object): object;
renameProps(rules: object): (input: object) => object;
renameProps<Output>(rules: object, input: object): Output;
renameProps<Output>(rules: object): (input: object) => Output;
Tests
import { renameProps } from './renameProps'

test('renameProps', () => {
  const rules = {
    f : 'foo',
    b : 'bar',
  }
  const input = {
    f : 1,
    b : 2,
  }
  const result = renameProps(rules, input)
  const expectedResult = {
    foo : 1,
    bar : 2,
  }
  expect(result).toEqual(expectedResult)
})

test('curry', () => {
  const rules = {
    f : 'foo',
    b : 'bar',
  }
  const input = {
    f : 1,
    b : 2,
  }
  const result = renameProps(rules)(input)
  const expectedResult = {
    foo : 1,
    bar : 2,
  }
  expect(result).toEqual(expectedResult)
})

repeat

repeat<T>(x: T): (timesToRepeat: number) => T[]

It returns a list of x input repeated timesToRepeat input.

R.repeat('foo', 3)
// => ['foo', 'foo', 'foo']

Try the above R.repeat example in Rambda REPL

All Typescript definitions
repeat<T>(x: T): (timesToRepeat: number) => T[];
repeat<T>(x: T, timesToRepeat: number): T[];
Tests
import { repeat } from './repeat'

test('repeat', () => {
  expect(repeat('')(3)).toEqual([ '', '', '' ])
  expect(repeat('foo', 3)).toEqual([ 'foo', 'foo', 'foo' ])

  const obj = {}
  const arr = repeat(obj, 3)

  expect(arr).toEqual([ {}, {}, {} ])

  expect(arr[ 0 ] === arr[ 1 ]).toBeTrue()
})

replace

replace(strOrRegex: RegExp | string, replacer: string, str: string): string

It replaces strOrRegex found in str with replacer.

const strOrRegex = /o/g

const result = R.replace(strOrRegex, '|0|', 'foo')
// => 'f|0||0|'

Try the above R.replace example in Rambda REPL

All Typescript definitions
replace(strOrRegex: RegExp | string, replacer: string, str: string): string;
replace(strOrRegex: RegExp | string, replacer: string): (str: string) => string;
replace(strOrRegex: RegExp | string): (replacer: string) => (str: string) => string;
Tests
import { replace } from './replace'

test('happy', () => {
  expect(replace(
    'foo', 'yes', 'foo bar baz'
  )).toEqual('yes bar baz')
})

test('1', () => {
  expect(replace(/\s/g)('|')('foo bar baz')).toEqual('foo|bar|baz')
})

test('2', () => {
  expect(replace(/\s/g)('|', 'foo bar baz')).toEqual('foo|bar|baz')
})

test('3', () => {
  expect(replace(/\s/g, '|')('foo bar baz')).toEqual('foo|bar|baz')
})

reset

reset(): void
All Typescript definitions
reset(): void;

reverse

reverse<T>(listOrString: ReadonlyArray<T>): T[]

It returns a reversed copy of listOrString input.

const result = [
  R.reverse('foo'),
  R.reverse([1, 2, 3])
]
// => ['oof', [3, 2, 1]

Try the above R.reverse example in Rambda REPL

All Typescript definitions
reverse<T>(listOrString: ReadonlyArray<T>): T[];
reverse(listOrString: string): string;
Tests
import { reverse } from './reverse'

test('happy', () => {
  expect(reverse([ 1, 2, 3 ])).toEqual([ 3, 2, 1 ])
})

test('with string', () => {
  expect(reverse('baz')).toEqual('zab')
})

test('it doesn\'t mutate', () => {
  const arr = [ 1, 2, 3 ]

  expect(reverse(arr)).toEqual([ 3, 2, 1 ])

  expect(arr).toEqual([ 1, 2, 3 ])
})

set

set<T, U>(lens: Lens, replacer: U, obj: T): T

It returns a copied Object or Array with modified lens focus set to replacer value.

const input = {x: 1, y: 2}
const xLens = R.lensProp('x')

R.set(xLens, 4, input) //=> {x: 4, y: 2}
R.set(xLens, 8, input) //=> {x: 8, y: 2}

Try the above R.set example in Rambda REPL

All Typescript definitions
set<T, U>(lens: Lens, replacer: U, obj: T): T;
set<U>(lens: Lens, replacer: U): <T>(obj: T) => T;
set(lens: Lens): <T, U>(replacer: U, obj: T) => T;

setter

setter(keyOrObject: string | object, value?: any): void
All Typescript definitions
setter(keyOrObject: string | object, value?: any): void;

shuffle

shuffle<T>(list: T[]): T[]

It returns a randomized copy of array.

All Typescript definitions
shuffle<T>(list: T[]): T[];
Tests
import { range } from './range'
import { shuffle } from './shuffle'
import { uniq } from './uniq'

test('happy', () => {
  const list = range(0, 7)
  const result = range(0, 300).map(() => shuffle(list))
  const allUniq = uniq(result)
  expect(allUniq.length > 150).toBeTrue()
})

slice

slice(from: number, to: number, list: string): string

It returns listOrString between from and to indexes.

const list = [0, 1, 2, 3, 4, 5]
const str = 'FOO_BAR'
const from = 1
const to = 4

const result = [
  R.slice(str, to, list),
  R.slice(from, to, list)
]
// => ['OO_', [1, 2, 3]]

Try the above R.slice example in Rambda REPL

All Typescript definitions
slice(from: number, to: number, list: string): string;
slice<T>(from: number, to: number, list: T[]): T[];
slice(from: number, to: number): {
  (list: string): string;
  <T>(list: T[]): T[];
};
slice(from: number): {
  (to: number, list: string): string;
  <T>(to: number, list: T[]): T[];
};
Tests
import { slice } from './slice'

test('slice', () => {
  expect(slice(
    1, 3, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    1, Infinity, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c', 'd' ])
  expect(slice(
    0, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'a', 'b', 'c' ])
  expect(slice(
    -3, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    0, 3, 'ramda'
  )).toEqual('ram')
})

sort

sort<T>(sortFn: (a: T, b: T) => number, list: ReadonlyArray<T>): T[]

It returns copy of list sorted by sortFn function.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = (x, y) => {
  return x.a > y.a ? 1 : -1
}

const result = R.sort(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

Try the above R.sort example in Rambda REPL

All Typescript definitions
sort<T>(sortFn: (a: T, b: T) => number, list: ReadonlyArray<T>): T[];
sort<T>(sortFn: (a: T, b: T) => number): (list: ReadonlyArray<T>) => T[];
Tests
import { sort } from './sort'

const fn = (a, b) => a > b ? 1 : -1

test('sort', () => {
  expect(sort((a, b) => a - b)([ 2, 3, 1 ])).toEqual([ 1, 2, 3 ])
})

test('it doesn\'t mutate', () => {
  const list = [ 'foo', 'bar', 'baz' ]

  expect(sort(fn, list)).toEqual([ 'bar', 'baz', 'foo' ])

  expect(list[ 0 ]).toBe('foo')
  expect(list[ 1 ]).toBe('bar')
  expect(list[ 2 ]).toBe('baz')
})

sortBy

sortBy<T>(sortFn: (a: T) => Ord, list: ReadonlyArray<T>): T[]

It returns copy of list sorted by sortFn function.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = x => x.a

const result = R.sortBy(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

Try the above R.sortBy example in Rambda REPL

All Typescript definitions
sortBy<T>(sortFn: (a: T) => Ord, list: ReadonlyArray<T>): T[];
sortBy(sortFn: (a: any) => Ord): <T>(list: ReadonlyArray<T>) => T[];
Tests
import { compose } from './compose'
import { prop } from './prop'
import { sortBy } from './sortBy'
import { toLower } from './toLower'

test('happy', () => {
  const input = [ { a : 2 }, { a : 1 }, { a : 1 }, { a : 3 } ]
  const expected = [ { a : 1 }, { a : 1 }, { a : 2 }, { a : 3 } ]

  const result = sortBy(x => x.a)(input)
  expect(result).toEqual(expected)
})

test('with compose', () => {
  const alice = {
    name : 'ALICE',
    age  : 101,
  }
  const bob = {
    name : 'Bob',
    age  : -10,
  }
  const clara = {
    name : 'clara',
    age  : 314.159,
  }
  const people = [ clara, bob, alice ]
  const sortByNameCaseInsensitive = sortBy(compose(toLower, prop('name')))

  expect(sortByNameCaseInsensitive(people)).toEqual([ alice, bob, clara ])
})

sortObject

sortObject<T>(predicate: SortObjectPredicate<T>, input: { [key: string]: T }): { [keyOutput: string]: T }

It returns a sorted version of input object.

const predicate = (propA, propB, valueA, valueB) => valueA > valueB ? -1 : 1

const result = R.sortObject(predicate, {a:1, b: 4, c: 2})
// => {b: 4, c: 2, a: 1}

Try the above R.sortObject example in Rambda REPL

All Typescript definitions
sortObject<T>(predicate: SortObjectPredicate<T>, input: { [key: string]: T }): { [keyOutput: string]: T };
sortObject<T>(predicate: SortObjectPredicate<T>): (input: { [key: string]: T }) => { [keyOutput: string]: T };
Tests
import { runTests } from 'helpers-fn'

import { allTrue } from './allTrue'
import { equals } from './equals'
import { sortObject } from './sortObject'

const obj = {
  c : 1,
  a : 2,
  b : 3,
}

const predicateA = (
  propA, propB, valueA, valueB
) => propA > propB ? -1 : 1

const expectationA = [ 'c', 'b', 'a' ]

const predicateB = (
  propA, propB, valueA, valueB
) => propA < propB ? -1 : 1
const expectationB = [ 'a', 'b', 'c' ]
const predicateC = (
  propA, propB, valueA, valueB
) =>
  valueA > valueB ? -1 : 1
const expectationC = [ 'b', 'a', 'c' ]

const fn = ([ predicate, expectation ]) => {
  const result = sortObject(predicate, obj)
  const curriedResult = sortObject(predicate)(obj)
  const sortedKeys = Object.keys(result)
  const sortedKeysCurried = Object.keys(curriedResult)
  const isSameObject = equals(obj, result)
  const isSameObjectCurried = equals(obj, curriedResult)

  return allTrue(
    isSameObject,
    isSameObjectCurried,
    equals(sortedKeys, expectation),
    equals(sortedKeysCurried, expectation)
  )
}

const testData = {
  label : 'foo',
  data  : [
    { ok : [ predicateA, expectationA ] },
    { ok : [ predicateB, expectationB ] },
    { ok : [ predicateC, expectationC ] },
  ],
  fn,
}

runTests(testData)

split

split(separator: string | RegExp): (str: string) => string[]

Curried version of String.prototype.split

const str = 'foo|bar|baz'
const separator = |'
const result = R.split(separator, str))
// => [ 'foo', 'bar', 'baz' ]

Try the above R.split example in Rambda REPL

All Typescript definitions
split(separator: string | RegExp): (str: string) => string[];
split(separator: string | RegExp, str: string): string[];
Tests
import { split } from './split'

const str = 'foo|bar|baz'
const splitChar = '|'
const expected = [ 'foo', 'bar', 'baz' ]

test('happy', () => {
  expect(split(splitChar, str)).toEqual(expected)
})

test('curried', () => {
  expect(split(splitChar)(str)).toEqual(expected)
})

splitEvery

splitEvery<T>(sliceLength: number, listOrString: ReadonlyArray<T>): T[][]

It splits listOrString into slices of sliceLength.

const result = [
  R.splitEvery(2, [1, 2, 3]), 
  R.splitEvery(3, 'foobar') 
]

const expected = [
  [[1, 2], [3]],
  ['foo', 'bar']
]
// => `result` is equal to `expected`

Try the above R.splitEvery example in Rambda REPL

All Typescript definitions
splitEvery<T>(sliceLength: number, listOrString: ReadonlyArray<T>): T[][];
splitEvery(sliceLength: number, listOrString: string): string[];
splitEvery(sliceLength: number): {
  (listOrString: string): string[];
  <T>(listOrString: ReadonlyArray<T>): T[][];
};
Tests
import { splitEvery } from './splitEvery'

test('happy', () => {
  expect(splitEvery(3, [ 1, 2, 3, 4, 5, 6, 7 ])).toEqual([
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7 ],
  ])

  expect(splitEvery(3)('foobarbaz')).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with bad input', () => {
  expect(() =>
    expect(splitEvery(0)('foo')).toEqual([ 'f', 'o', 'o' ])).toThrowWithMessage(Error,
    'First argument to splitEvery must be a positive integer')
})

startsWith

startsWith(target: string, str: string): boolean

Curried version of String.prototype.startsWith

const str = 'foo-bar'

const result = [
  R.startsWith('foo', str),
  R.startsWith('bar', str)
]
// => [true, false]

Try the above R.startsWith example in Rambda REPL

All Typescript definitions
startsWith(target: string, str: string): boolean;
startsWith(target: string): (str: string) => boolean;
Tests
import { startsWith } from './startsWith'

test('true', () => {
  const result = startsWith('foo', 'foo-bar')

  expect(result).toBeTrue()
})

test('false', () => {
  const result = startsWith('baz')('foo-bar')

  expect(result).toBeFalse()
})

subtract

subtract(x: number, y: number): number

Curried version of x - y

const x = 3
const y = 1

R.subtract(x, y) 
// => 2

Try the above R.subtract example in Rambda REPL

All Typescript definitions
subtract(x: number, y: number): number;
subtract(x: number): (y: number) => number;
Tests
import { subtract } from './subtract'

test('happy', () => {
  expect(subtract(2, 1)).toEqual(1)
  expect(subtract(2)(1)).toEqual(1)
})

sum

sum(list: ReadonlyArray<number>): number
R.sum([1, 2, 3, 4, 5]) 
// => 15

Try the above R.sum example in Rambda REPL

All Typescript definitions
sum(list: ReadonlyArray<number>): number;
Tests
import { sum } from './sum'

test('happy', () => {
  expect(sum([ 1, 2, 3, 4, 5 ])).toBe(15)
})

switcher

switcher<T>(valueToMatch: any): Switchem<T>

Edited fork of Switchem library.

The method return a value if the matched option is a value.

If the matched option is a function, then R.switcher returns a function which expects input. Tests of the method explain it better than this short description.

const valueToMatch = {foo: 1}

const result = R.switcher(valueToMatch)
  .is('baz', 'is baz')
  .is(x => typeof x === 'boolean', 'is boolean')
  .is({foo: 1}, 'Property foo is 1')
  .default('is bar')

// => 'Property foo is 1'

Try the above R.switcher example in Rambda REPL

All Typescript definitions
switcher<T>(valueToMatch: any): Switchem<T>;
Tests
import { add } from './add'
import { delay } from './delay'
import { identity } from './identity'
import { switcher } from './switcher'
import { tap } from './tap'
import { trim } from './trim'
import { type } from './type'

test('happy', () => {
  const a = true
  const b = false
  const result = switcher([ a, b ])
    .is([ false, false ], '0')
    .is([ false, true ], '1')
    .is([ true, true ], '2')
    .default('3')

  expect(result).toEqual('3')
})

test('can compare objects', () => {
  const result = switcher({ a : 1 })
    .is({ a : 1 }, 'it is object')
    .is('baz', 'it is baz')
    .default('it is default')

  expect(result).toEqual('it is object')
})

test('options are mixture of functions and values - input match function', () => {
  const fn = switcher('foo').is('bar', 1)
    .is('foo', add(1))
    .default(1000)

  expect(fn(2)).toEqual(3)
})

test('options are mixture of functions and values - input match value', () => {
  const result = switcher('bar').is('bar', 1)
    .is('foo', add(1))
    .default(1000)

  expect(result).toBe(1)
})

test('return function if all options are functions', () => {
  const fn = switcher('foo').is('bar', tap)
    .is('foo', add(1))
    .default(trim)

  expect(fn(2)).toEqual(3)
})

const switchFn = input =>
  switcher(input)
    .is(x => x.length && x.length === 7, 'has length of 7')
    .is('baz', 'it is baz')
    .default('it is default')

test('works with function as condition', () => {
  expect(switchFn([ 0, 1, 2, 3, 4, 5, 6 ])).toEqual('has length of 7')
})

test('works with string as condition', () => {
  expect(switchFn('baz')).toEqual('it is baz')
})

test('fallback to default input when no matches', () => {
  expect(switchFn(1)).toEqual('it is default')
})

symmetricDifference

symmetricDifference<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[]

It returns a merged list of x and y with all equal elements removed.

const x = [ 1, 2, 3, 4 ]
const y = [ 3, 4, 5, 6 ]

const result = symmetricDifference(x, y)
// => [ 1, 2, 5, 6 ]

Try the above R.symmetricDifference example in Rambda REPL

All Typescript definitions
symmetricDifference<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[];
symmetricDifference<T>(x: ReadonlyArray<T>): <T>(y: ReadonlyArray<T>) => T[];
Tests
import { symmetricDifference } from './symmetricDifference'

test('symmetricDifference', () => {
  const list1 = [ 1, 2, 3, 4 ]
  const list2 = [ 3, 4, 5, 6 ]
  expect(symmetricDifference(list1)(list2)).toEqual([ 1, 2, 5, 6 ])

  expect(symmetricDifference([], [])).toEqual([])
})

test('symmetricDifference with objects', () => {
  const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(symmetricDifference(list1)(list2)).toEqual([
    { id : 1 },
    { id : 2 },
    { id : 5 },
    { id : 6 },
  ])
})

T

T(): boolean
R.T() 
// => true

Try the above R.T example in Rambda REPL

All Typescript definitions
T(): boolean;

tail

tail<T>(listOrString: ReadonlyArray<T>): T[]

It returns all but the first element of listOrString.

const result = [
  R.tail([1, 2, 3]),  
  R.tail('foo') 
]
// => [[2, 3], 'oo']

Try the above R.tail example in Rambda REPL

All Typescript definitions
tail<T>(listOrString: ReadonlyArray<T>): T[];
tail(listOrString: string): string;
Tests
import { tail } from './tail'

test('tail', () => {
  expect(tail([ 1, 2, 3 ])).toEqual([ 2, 3 ])
  expect(tail([ 1, 2 ])).toEqual([ 2 ])
  expect(tail([ 1 ])).toEqual([])
  expect(tail([])).toEqual([])

  expect(tail('abc')).toEqual('bc')
  expect(tail('ab')).toEqual('b')
  expect(tail('a')).toEqual('')
  expect(tail('')).toEqual('')
})

take

take<T>(howMany: number, listOrString: ReadonlyArray<T>): T[]

It returns the first howMany elements of listOrString.

const howMany = 2

const result = [
  R.take(howMany, [1, 2, 3]),
  R.take(howMany, 'foobar'),
]
// => [[1, 2], 'fo']

Try the above R.take example in Rambda REPL

All Typescript definitions
take<T>(howMany: number, listOrString: ReadonlyArray<T>): T[];
take(howMany: number, listOrString: string): string;
take<T>(howMany: number): {
  <T>(listOrString: readonly T[]): T[];
  (listOrString: string): string;
};
Tests
import { take } from './take'

test('happy', () => {
  const arr = [ 'foo', 'bar', 'baz' ]

  expect(take(1, arr)).toEqual([ 'foo' ])

  expect(arr).toEqual([ 'foo', 'bar', 'baz' ])

  expect(take(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar' ])
  expect(take(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(3)('rambda')).toEqual('ram')
})

test('with negative index', () => {
  expect(take(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(take(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('with zero index', () => {
  expect(take(0, [ 1, 2, 3 ])).toEqual([])
})

takeLast

takeLast<T>(howMany: number, listOrString: ReadonlyArray<T>): T[]

It returns the last howMany elements of listOrString.

const howMany = 2

const result = [
  R.takeLast(howMany, [1, 2, 3]),
  R.takeLast(howMany, 'foobar'),
]
// => [[2, 3], 'ar']

Try the above R.takeLast example in Rambda REPL

All Typescript definitions
takeLast<T>(howMany: number, listOrString: ReadonlyArray<T>): T[];
takeLast(howMany: number, listOrString: string): string;
takeLast<T>(howMany: number): {
  <T>(listOrString: readonly T[]): T[];
  (listOrString: string): string;
};
Tests
import { takeLast } from './takeLast'

test('with arrays', () => {
  expect(takeLast(1, [ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])

  expect(takeLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'bar', 'baz' ])

  expect(takeLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(10, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with strings', () => {
  expect(takeLast(3, 'rambda')).toEqual('bda')

  expect(takeLast(7, 'rambda')).toEqual('rambda')
})

test('with negative index', () => {
  expect(takeLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(takeLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

tap

tap<T>(fn: (a: T) => any, x: T): T

It applies function fn to input x and returns x.

One use case is debuging in the middle of R.compose.

const list = [1, 2, 3]

R.compose(
  R.map(x => x * 2)
  R.tap(console.log),
  R.filter(x => x > 1)
)(list)
// => `2` and `3` will be logged

Try the above R.tap example in Rambda REPL

All Typescript definitions
tap<T>(fn: (a: T) => any, x: T): T;
tap<T>(fn: (a: T) => any): (x: T) => T;
Tests
import { tap } from './tap'

test('tap', () => {
  let a = 1
  const sayX = x => a = x

  expect(tap(sayX, 100)).toEqual(100)
  expect(tap(sayX)(100)).toEqual(100)
  expect(a).toEqual(100)
})

tapAsync

tapAsync<T>(fn: Func<any> | Promise<any>, input: T): T

Asynchronous version of R.tap.

All Typescript definitions
tapAsync<T>(fn: Func<any> | Promise<any>, input: T): T;
tapAsync<T>(fn: Func<any> | Promise<any>): (input: T) => T;
Tests
import { delay } from './delay'
import { tapAsync } from './tapAsync'

test('', async () => {
  const result = await tapAsync(delay)(1)
  expect(result).toEqual(1)
})

template

template(inputWithTags: string, templateArguments: object): string

It generages a new string from inputWithTags by replacing all {{x}} occurances with values provided by templateArguments.

const inputWithTags = 'foo is {{bar}} even {{a}} more'
const templateArguments = {"bar":"BAR", a: 1}

const result = R.template(inputWithTags, templateArguments)
const expected = 'foo is BAR even 1 more'
// => `result` is equal to `expected`

Try the above R.template example in Rambda REPL

All Typescript definitions
template(inputWithTags: string, templateArguments: object): string;
template(inputWithTags: string): (templateArguments: object) => string;
Tests
import { template } from './template'

test('within bracets', () => {
  const input = 'foo is { {{bar}} } even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = template(input, templateInput)
  const expectedResult = 'foo is { BAR } even 1 more'

  expect(result).toEqual(expectedResult)
})

test('happy', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = template(input, templateInput)
  const expectedResult = 'foo is BAR even 1 more'

  expect(result).toEqual(expectedResult)
})

test('no interpolation + curry', () => {
  const input = 'foo is bar even more'
  const templateInput = { bar : 'BAR' }

  const result = template(input)(templateInput)
  const expectedResult = 'foo is bar even more'

  expect(result).toEqual(expectedResult)
})

test('with missing template input', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    baz : 'BAR',
    a   : 1,
  }

  const result = template(input, templateInput)
  const expectedResult = 'foo is {{bar}} even 1 more'

  expect(result).toEqual(expectedResult)
})

test('with arbitrary expression', () => {
  const input = '1 + 2 = {{ 1 + 2 }}'
  const templateInput = {}

  const expectedResult = '1 + 2 = 3'
  const result = template(input, templateInput)

  expect(result).toEqual(expectedResult)
})

test

test(regExpression: RegExp): (str: string) => boolean

It determines whether str matches regExpression.

R.test(/^f/, 'foo')
// => true

Try the above R.test example in Rambda REPL

All Typescript definitions
test(regExpression: RegExp): (str: string) => boolean;
test(regExpression: RegExp, str: string): boolean;
Tests
import { test as testMethod } from './test'

test('happy', () => {
  expect(testMethod(/^x/, 'xyz')).toBeTrue()

  expect(testMethod(/^y/)('xyz')).toBeFalse()
})

test('throws if first argument is not regex', () => {
  expect(() => testMethod('foo', 'bar')).toThrowWithMessage(TypeError,
    '‘test’ requires a value of type RegExp as its first argument; received "foo"')
})

throttle

throttle<T, U>(fn: (input: T) => U, ms: number): (input: T) => U

It creates a throttled function that invokes fn maximum once for a period of milliseconds.

let counter = 0
const inc = () => {
  counter++
}

const throttledInc = R.throttle(inc, 800)

const result = async () => {
  throttledInc()
  await R.delay(500)
  throttledInc()

  return counter
}
// `result` resolves to `1`

Try the above R.throttle example in Rambda REPL

All Typescript definitions
throttle<T, U>(fn: (input: T) => U, ms: number): (input: T) => U;
throttle<T, Q, U>(fn: (input1: T, input2: Q) => U, ms: number): (input1: T, input2: Q) => U;
throttle<T, Q, Z, U>(fn: (input1: T, input2: Q, input3: Z) => U, ms: number): (input1: T, input2: Q, input3: Z) => U;
Tests
import { delay } from './delay'
import { throttle } from './throttle'

test('', async () => {
  let counter = 0
  let aHolder
  let bHolder

  const inc = (a, b) => {
    aHolder = a
    bHolder = b
    counter++
  }

  const incWrapped = throttle(inc, 1000)

  incWrapped(1, 2)

  await delay(500)

  incWrapped(2, 3)
  incWrapped(3, 4)

  expect(counter).toBe(1)
  expect(aHolder).toBe(1)
  expect(bHolder).toBe(2)

  await delay(1000)

  incWrapped(5, 6)

  expect(counter).toBe(2)
  expect(aHolder).toBe(5)
  expect(bHolder).toBe(6)
})

times

times<T>(fn: (i: number) => T, howMany: number): T[]

It returns the result of applying function fn over members of range array.

The range array includes numbers between 0 and howMany(exclusive).

const fn = x => x * 2
const howMany = 5

R.times(fn, howMany)
//=> [0, 2, 4, 6, 8]

Try the above R.times example in Rambda REPL

All Typescript definitions
times<T>(fn: (i: number) => T, howMany: number): T[];
times<T>(fn: (i: number) => T): (howMany: number) => T[];
Tests
import assert from 'assert'

import { identity } from './identity'
import { times } from './times'

test('happy', () => {
  const result = times(identity, 5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

test('with bad input', () => {
  assert.throws(() => {
    times(3)('cheers!')
  }, RangeError)
  assert.throws(() => {
    times(identity, -1)
  }, RangeError)
})

test('curry', () => {
  const result = times(identity)(5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

toDecimal

toDecimal(num: number, charsAfterDecimalPoint?: number): number
R.toDecimal(2.45464,2) // => 2.45

Try the above R.toDecimal example in Rambda REPL

All Typescript definitions
toDecimal(num: number, charsAfterDecimalPoint?: number): number;
Tests
import { toDecimal } from './toDecimal'

test('', () => {
  expect(toDecimal(2.2789, 1)).toBe(2.3)
  expect(toDecimal(2.2789, 3)).toBe(2.279)
  expect(toDecimal(2.2789)).toBe(2.28)
  expect(toDecimal(2.45464)).toBe(2.45)
})

toLower

toLower(str: string): string
R.toLower('FOO')
// => 'foo'

Try the above R.toLower example in Rambda REPL

All Typescript definitions
toLower(str: string): string;
Tests
import { toLower } from './toLower'

test('toLower', () => {
  expect(toLower('FOO|BAR|BAZ')).toEqual('foo|bar|baz')
})

toPairs

toPairs<S>(obj: { [k: string]: S } | { [k: number]: S }): [string, S][]

It transforms an object to a list.

const list = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]

const result = R.toPairs(list)
// => `result` is equal to `expected`

Try the above R.toPairs example in Rambda REPL

All Typescript definitions
toPairs<S>(obj: { [k: string]: S } | { [k: number]: S }): [string, S][];
Tests
import { toPairs } from './toPairs'

const obj = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [
  [ 'a', 1 ],
  [ 'b', 2 ],
  [ 'c', [ 3, 4 ] ],
]

test('happy', () => {
  expect(toPairs(obj)).toEqual(expected)
})

toString

toString<T>(x: T): string
R.toString([1, 2]) 
// => '1,2'

Try the above R.toString example in Rambda REPL

All Typescript definitions
toString<T>(x: T): string;
Tests
import { toString } from './toString'

test('happy', () => {
  expect(toString([ 1, 2, 3 ])).toEqual('1,2,3')
})

toUpper

toUpper(str: string): string
R.toUpper('foo')
// => 'FOO'

Try the above R.toUpper example in Rambda REPL

All Typescript definitions
toUpper(str: string): string;
Tests
import { toUpper } from './toUpper'

test('toUpper', () => {
  expect(toUpper('foo|bar|baz')).toEqual('FOO|BAR|BAZ')
})

transpose

transpose<T>(list: T[][]): T[][]
const list = [[10, 11], [20], [], [30, 31, 32]]
const expected = [[10, 20, 30], [11, 31], [32]]

const result = R.transpose(list)
// => `result` is equal to `expected`

Try the above R.transpose example in Rambda REPL

All Typescript definitions
transpose<T>(list: T[][]): T[][];
Tests
import { transpose } from './transpose'

test('happy', () => {
  const input = [
    [ 'a', 1 ],
    [ 'b', 2 ],
    [ 'c', 3 ],
  ]

  expect(transpose(input)).toEqual([
    [ 'a', 'b', 'c' ],
    [ 1, 2, 3 ],
  ])
})

test('when rows are shorter', () => {
  const actual = transpose([ [ 10, 11 ], [ 20 ], [], [ 30, 31, 32 ] ])
  const expected = [ [ 10, 20, 30 ], [ 11, 31 ], [ 32 ] ]
  expect(actual).toEqual(expected)
})

test('with empty array', () => {
  expect(transpose([])).toEqual([])
})

test('array with falsy values', () => {
  const actual = transpose([
    [ true, false, undefined, null ],
    [ null, undefined, false, true ],
  ])
  const expected = [
    [ true, null ],
    [ false, undefined ],
    [ undefined, false ],
    [ null, true ],
  ]
  expect(actual).toEqual(expected)
})

trim

trim(str: string): string
R.trim('  foo  ') 
// => 'foo'

Try the above R.trim example in Rambda REPL

All Typescript definitions
trim(str: string): string;
Tests
import { trim } from './trim'

test('trim', () => {
  expect(trim(' foo ')).toEqual('foo')
})

tryCatch

tryCatch<T, U>(
  fn: (input: T) => U,
  fallback: U
): (input: T) => U

It returns function that runs fn in try/catch block. If there was an error, then fallback is used to return the result. Note that fn can be value or asynchronous/synchronous function(unlike Ramda where fallback can only be a synchronous function).

Please check the tests of R.tryCatch to fully understand how this method works.

const fn = x => x.foo

const result = [
  R.tryCatch(fn, false)(null),
  R.tryCatch(fn, false)({foo: 'bar'})
]
// => [false, 'bar']

Try the above R.tryCatch example in Rambda REPL

All Typescript definitions
tryCatch<T, U>(
  fn: (input: T) => U,
  fallback: U
): (input: T) => U;
tryCatch<T, U>(
  fn: (input: T) => U,
  fallback: (input: T) => U
): (input: T) => U;
tryCatch<T>(
  fn: (input: any) => Promise<any>,
  fallback: T
): (input: any) => Promise<T>;
tryCatch<T>(
  fn: (input: any) => Promise<any>,
  fallback: (input: any) => Promise<any>,
): (input: any) => Promise<T>;
Tests
import { delay } from './delay'
import { prop } from './prop'
import { tryCatch } from './tryCatch'

test('throws when fn is not function', () => {
  const fn = 'foo'

  expect(() => tryCatch(fn, false)(null)).toThrowWithMessage(Error,
    'R.tryCatch | fn \'foo\'')
})

test('when fallback is used', () => {
  const fn = x => x.x

  expect(tryCatch(fn, false)(null)).toBeFalse()
})

test('with json parse', () => {
  const good = () => JSON.parse(JSON.stringify({ a : 1 }))
  const bad = () => JSON.parse('a{a')

  expect(tryCatch(good, 1)(null)).toEqual({ a : 1 })
  expect(tryCatch(bad, 1)(null)).toBe(1)
})

test('when fallback is function', () => {
  const fn = x => x.x

  expect(tryCatch(fn, () => 1)(null)).toBe(1)
})

test('when fn is used', () => {
  const fn = prop('x')

  expect(tryCatch(fn, false)({})).toBe(undefined)
  expect(tryCatch(fn, false)({ x : 1 })).toBe(1)
})

test('fallback receives error object and all initial inputs', () => {
  function thrower(
    a, b, c
  ){
    void c
    throw new Error('throwerError')
  }

  function catchFn(
    e, a, b, c
  ){
    return [ e.message, a, b, c ].join('|')
  }

  const willThrow = tryCatch(thrower, catchFn)
  const result = willThrow(
    'A', 'B', 'C'
  )
  expect(result).toBe('throwerError|A|B|C')
})

test('fallback receives error object', () => {
  function throwFn(){
    throw new Error(10)
  }

  function eCatcher(
    e, a, b
  ){
    return e.message
  }

  const willThrow = tryCatch(throwFn, eCatcher)
  expect(willThrow([])).toBe('10')
  expect(willThrow([ {}, {}, {} ])).toBe('10')
})

test('when async + fallback', async () => {
  let called = false

  const fn = async input => {
    await delay(input)
    called = true

    return JSON.parse('{a:')
  }

  expect(await tryCatch(fn, 'fallback')(100)).toBe('fallback')
  expect(called).toBeTrue()
})

test('when async + fallback is function', async () => {
  let called = false

  const fn = async input => {
    await delay(input)
    called = true

    return JSON.parse('{a:')
  }

  expect(await tryCatch(fn, x => x + 1)(100)).toBe(101)
  expect(called).toBeTrue()
})

test('when async + fallback is async', async () => {
  let called = false
  const fn = async input => {
    await delay(input)
    called = true

    return JSON.parse('{a:')
  }
  const fallback = async input => {
    await delay(10)

    return input + 1
  }

  expect(await tryCatch(fn, fallback)(100)).toBe(101)
  expect(called).toBeTrue()
})

test('when async + fn', async () => {
  let called = false

  const fn = async input => {
    await delay(input)
    called = true

    return input + 1
  }

  expect(await tryCatch(fn, 'fallback')(100)).toBe(101)
  expect(called).toBeTrue()
})

type

type(x: any): "Object" | "Number" | "Boolean" | "String" | "Null" | "Array" | "Function" | "Undefined" | "Async" | "Promise" | "RegExp" | "NaN"

It accepts any input and it returns its type.

R.type(() => {}) // => 'Function'
R.type(async () => {}) // => 'Async'
R.type([]) // => 'Array'
R.type({}) // => 'Object'
R.type('foo') // => 'String'
R.type(1) // => 'Number'
R.type(true) // => 'Boolean'
R.type(null) // => 'Null'
R.type(/[A-z]/) // => 'RegExp'
R.type('foo'*1) // => 'NaN'

const delay = ms => new Promise(resolve => {
  setTimeout(function () {
    resolve()
  }, ms)
})
R.type(delay) // => 'Promise'

Try the above R.type example in Rambda REPL

All Typescript definitions
type(x: any): "Object" | "Number" | "Boolean" | "String" | "Null" | "Array" | "Function" | "Undefined" | "Async" | "Promise" | "RegExp" | "NaN";
Tests
import { type as ramdaType } from 'ramda'

import { type } from './type'

test('with simple promise', () => {
  expect(type(Promise.resolve(1))).toBe('Promise')
})

test('with new Boolean', () => {
  expect(type(new Boolean(true))).toBe('Boolean')
})

test('with new String', () => {
  expect(type(new String('I am a String object'))).toEqual('String')
})

test('with new Number', () => {
  expect(type(new Number(1))).toBe('Number')
})

test('with new promise', () => {
  const delay = ms =>
    new Promise(resolve => {
      setTimeout(() => {
        resolve(ms + 110)
      }, ms)
    })

  expect(type(delay(10))).toEqual('Promise')
})

test('async function', () => {
  expect(type(async () => {})).toEqual('Async')
})

test('async arrow', () => {
  const asyncArrow = async () => {}
  expect(type(asyncArrow)).toBe('Async')
})

test('function', () => {
  const fn1 = () => {}
  const fn2 = function (){}

  function fn3(){}

  ;[ () => {}, fn1, fn2, fn3 ].map(val => {
    expect(type(val)).toEqual('Function')
  })
})

test('object', () => {
  expect(type({})).toEqual('Object')
})

test('number', () => {
  expect(type(1)).toEqual('Number')
})

test('boolean', () => {
  expect(type(false)).toEqual('Boolean')
})

test('string', () => {
  expect(type('foo')).toEqual('String')
})

test('null', () => {
  expect(type(null)).toEqual('Null')
})

test('array', () => {
  expect(type([])).toEqual('Array')
  expect(type([ 1, 2, 3 ])).toEqual('Array')
})

test('regex', () => {
  expect(type(/\s/g)).toEqual('RegExp')
})

test('undefined', () => {
  expect(type(undefined)).toEqual('Undefined')
})

test('not a number', () => {
  expect(type(Number('s'))).toBe('NaN')
})

test('function inside object 1', () => {
  const obj = {
    f(){
      return 4
    },
  }

  expect(type(obj.f)).toBe('Function')
  expect(ramdaType(obj.f)).toBe('Function')
})

test('function inside object 2', () => {
  const name = 'f'
  const obj = {
    [ name ](){
      return 4
    },
  }
  expect(type(obj.f)).toBe('Function')
  expect(ramdaType(obj.f)).toBe('Function')
})

uniq

uniq<T>(list: ReadonlyArray<T>): T[]

It returns a new array containing only one copy of each element of list.

const list = [1, 1, {a: 1}, {a: 2}, {a:1}]

R.uniq(list)
// => [1, {a: 1}, {a: 2}]

Try the above R.uniq example in Rambda REPL

All Typescript definitions
uniq<T>(list: ReadonlyArray<T>): T[];
Tests
import { uniq } from './uniq'

test('uniq', () => {
  expect(uniq([ 1, 2, 3, 3, 3, 1, 2, 0 ])).toEqual([ 1, 2, 3, 0 ])
  expect(uniq([ 1, 1, 2, 1 ])).toEqual([ 1, 2 ])
  expect([ 1, '1' ]).toEqual([ 1, '1' ])
  expect(uniq([ [ 42 ], [ 42 ] ])).toEqual([ [ 42 ] ])
})

uniqWith

uniqWith<T, U>(uniqFn: (x: T, y: T) => boolean, list: ReadonlyArray<T>): T[]

It returns a new array containing only one copy of each element in list according to boolean returning function uniqFn.

const list = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
  {id: 3, title:'foo'},
  {id: 4, title:'bar'},
]

const expected = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
]

const uniqFn = (x,y) => x.title === y.title

const result = R.uniqWith(uniqFn, list)
// => `result` is equal to `expected`

Try the above R.uniqWith example in Rambda REPL

All Typescript definitions
uniqWith<T, U>(uniqFn: (x: T, y: T) => boolean, list: ReadonlyArray<T>): T[];
uniqWith<T, U>(uniqFn: (x: T, y: T) => boolean): (list: ReadonlyArray<T>) => T[];
Tests
import { uniqWith } from './uniqWith'

test('happy', () => {
  const input = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
    {
      id    : 3,
      title : 'foo',
    },
    {
      id    : 4,
      title : 'bar',
    },
  ]

  const expectedResult = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
  ]

  const fn = (x, y) => x.title === y.title

  const result = uniqWith(fn, input)
  const curriedResult = uniqWith(fn)(input)

  expect(result).toEqual(expectedResult)

  expect(curriedResult).toEqual(expectedResult)
})

test('uniqWith', () => {
  const input = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
    {
      id    : 3,
      title : 'foo',
    },
    {
      id    : 4,
      title : 'bar',
    },
  ]

  const expectedResult = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
  ]

  const fn = (x, y) => x.title === y.title

  const result = uniqWith(fn, input)
  //const result = uniqWith(Ramda.eqBy(Ramda.prop('title')), input)

  expect(result).toEqual(expectedResult)
})

unless

unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, obj: T): U

The method returns function that will be called with argument input.

If predicate(input) returns false, then the end result will be the outcome of whenFalse(input).

In the other case, the final output will be the input itself.

const fn = R.unless(
  x => x > 2,
  x => x + 10
)

const result = [
  fn(1),
  fn(5)
]
// => [11, 5]

Try the above R.unless example in Rambda REPL

All Typescript definitions
unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, obj: T): U;
unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U): (obj: T) => U;
Tests
import { inc } from './inc'
import { isNil } from './isNil'
import { unless } from './unless'

const safeInc = unless(isNil, inc)

test('happy', () => {
  expect(safeInc(null)).toBeNull()
  expect(safeInc(1)).toBe(2)
})

test('curried', () => {
  const safeIncCurried = unless(isNil)(inc)
  expect(safeIncCurried(null)).toBeNull()
  expect(safeIncCurried(1)).toBe(2)
})

update

update<T>(index: number, newValue: T, list: ReadonlyArray<T>): T[]

It returns a copy of list with updated element at index with newValue.

const index = 2
const newValue = 88
const list = [1, 2, 3, 4, 5]

const result = R.update(index, newValue, list)
// => [1, 2, 88, 4, 5]

Try the above R.update example in Rambda REPL

All Typescript definitions
update<T>(index: number, newValue: T, list: ReadonlyArray<T>): T[];
update<T>(index: number, newValue: T): (list: ReadonlyArray<T>) => T[];
Tests
import { update } from './update'

const list = [ 1, 2, 3 ]

test('happy', () => {
  const newValue = 8
  const index = 1
  const result = update(
    index, newValue, list
  )
  const curriedResult = update(index, newValue)(list)
  const tripleCurriedResult = update(index)(newValue)(list)

  const expected = [ 1, 8, 3 ]
  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
  expect(tripleCurriedResult).toEqual(expected)
})

test('list has no such index', () => {
  const newValue = 8
  const index = 10
  const result = update(
    index, newValue, list
  )

  expect(result).toEqual(list)
})

values

values<T extends object, K extends keyof T>(obj: T): T[K][]

With correct input, this is nothing more than Object.values(obj). If obj is not an object, then it returns an empty array.

const obj = {a:1, b:2}

R.values(obj)
// => [1, 2]

Try the above R.values example in Rambda REPL

All Typescript definitions
values<T extends object, K extends keyof T>(obj: T): T[K][];
Tests
import { values } from './values'

test('happy', () => {
  expect(values({
    a : 1,
    b : 2,
    c : 3,
  })).toEqual([ 1, 2, 3 ])
})

test('with bad input', () => {
  expect(values(null)).toEqual([])
  expect(values(undefined)).toEqual([])
  expect(values(55)).toEqual([])
  expect(values('foo')).toEqual([])
  expect(values(true)).toEqual([])
  expect(values(false)).toEqual([])
  expect(values(NaN)).toEqual([])
  expect(values(Infinity)).toEqual([])
  expect(values([])).toEqual([])
})

view

view<T, U>(lens: Lens): (target: T) => U

It returns the value of lens focus over target object.

const lens = R.lensProp('x')

R.view(lens, {x: 1, y: 2}) //=> 1
R.view(lens, {x: 4, y: 2}) //=> 4

Try the above R.view example in Rambda REPL

All Typescript definitions
view<T, U>(lens: Lens): (target: T) => U;
view<T, U>(lens: Lens, target: T): U;

wait

wait<T>(fn: Promise<T>): Promise<[T, Error|undefined]>

It provides Golang-like interface for handling promises.

const [result, err] = await R.wait(R.delay(1000))
// => err is undefined
// => result is `RAMBDAX_DELAY`

Try the above R.wait example in Rambda REPL

All Typescript definitions
wait<T>(fn: Promise<T>): Promise<[T, Error|undefined]>;
wait<T>(fn: (x: any) => Promise<T>): Promise<[T, Error|undefined]>;
Tests
import { wait } from './wait'

test('happy path', async () => {
  const fn = x => Promise.resolve(x + 1)
  const [ result, err ] = await wait(fn(1))

  expect(result).toBe(2)
  expect(err).toBeUndefined()
})

test('when promise is rejected', async () => {
  const fn = x => Promise.reject(Error('foo'))
  const [ result, err ] = await wait(fn(1))

  expect(result).toBeUndefined()
  expect(err).toEqual(Error('foo'))
})

waitFor

waitFor(
  waitForTrueCondition: () => boolean,
  howLong: number,
  loops?: number
): () => Promise<boolean>

It returns true, if condition returns true within howLong milisececonds time period.

The method accepts an optional third argument loops(default to 10), which is the number of times waitForTrueCondition will be evaluated for howLong period. Once this function returns a value different from false, this value will be the final result.

Otherwise, R.waitFor will return false.

const howLong = 1000
let counter = 0
const waitForTrueCondition = async x => {
  await R.delay(100)
  counter = counter + x

  return counter > 10
}

const result = await R.waitFor(waitForTrueCondition, howLong)(2)
// => true

Try the above R.waitFor example in Rambda REPL

All Typescript definitions
waitFor(
  waitForTrueCondition: () => boolean,
  howLong: number,
  loops?: number
): () => Promise<boolean>;
waitFor(
  waitForTrueCondition: () => Promise<boolean>,
  howLong: number,
  loops?: number
): () => Promise<boolean>;
waitFor<T>(
  waitForTrueCondition: (input: T) => Promise<boolean>,
  howLong: number,
  loops?: number
): (input: T) => Promise<boolean>;
waitFor<T>(
  waitForTrueCondition: (input: T) => boolean,
  howLong: number,
  loops?: number
): (input: T) => Promise<boolean>;

// RAMBDAX_MARKER_END
// ============================================

export as namespace R
Tests
import { delay } from './delay'
import { waitFor } from './waitFor'

const howLong = 1000

test('true', async () => {
  let counter = 0
  const condition = x => {
    counter++

    return counter > x
  }

  const result = await waitFor(condition, howLong)(6)
  expect(result).toEqual(true)
})

test('false', async () => {
  let counter = 0
  const condition = x => {
    counter++

    return counter > x
  }

  const result = await waitFor(condition, howLong)(12)
  expect(result).toEqual(false)
})

test('async condition | true', async () => {
  let counter = 0
  const condition = async x => {
    counter++
    await delay(10)

    return counter > x
  }

  const result = await waitFor(condition, howLong)(6)
  expect(result).toEqual(true)
})

test('async condition | false', async () => {
  let counter = 0
  const condition = async x => {
    counter++
    await delay(10)

    return counter > x
  }

  const result = await waitFor(condition, howLong)(12)
  expect(result).toEqual(false)
})

test('throws when fn is not function', () => {
  const fn = 'foo'

  expect(() => waitFor(fn, howLong)()).toThrowWithMessage(Error, 'R.waitFor')
})

when

when<T>(
  rule: Func<boolean>, resultOrFunction: T | IdentityFunction<T>
): IdentityFunction<T>
All Typescript definitions
when<T>(
  rule: Func<boolean>, resultOrFunction: T | IdentityFunction<T>
): IdentityFunction<T>;
when<T>(
  rule: Func<boolean>
): (resultOrFunction: T | IdentityFunction<T>) => IdentityFunction<T>;
Tests
import { add } from './add'
import { is } from './is'
import { when } from './when'

const ruleResult = 'RULE_RESULT'
const rule = x => typeof x === 'number'
const fn = when(rule, ruleResult)
const curriedFn = when(rule)(ruleResult)

test('when rule returns true', () => {
  const input = 7

  expect(fn(input)).toBe(ruleResult)
})

test('when rule returns false', () => {
  const input = 'foo'

  expect(fn(input)).toBe(input)
  expect(curriedFn(input)).toBe(input)
})

test('second argument can be a function', () => {
  const fn = when(is(Number), add(1))
  expect(fn(10)).toBe(11)
})

where

where<T, U>(conditions: T, input: U): boolean

It returns true if all each property in conditions returns true when applied to corresponding property in input object.

const condition = R.where({
  a : x => typeof x === "string",
  b : x => x === 4
})
const input = {
  a : "foo",
  b : 4,
  c : 11,
}

const result = condition(input) 
// => true

Try the above R.where example in Rambda REPL

All Typescript definitions
where<T, U>(conditions: T, input: U): boolean;
where<T>(conditions: T): <U>(input: U) => boolean;
where<ObjFunc2, U>(conditions: ObjFunc2, input: U): boolean;
where<ObjFunc2>(conditions: ObjFunc2): <U>(input: U) => boolean;
Tests
import { equals } from './equals'
import { where } from './where'

test('when true', () => {
  const predicate = where({
    a : equals('foo'),
    b : equals('bar'),
  })
  expect(predicate({
    a : 'foo',
    b : 'bar',
    x : 11,
    y : 19,
  })).toEqual(true)
})

test('when false', () => {
  const predicate = where({
    a : equals('foo'),
    b : equals('baz'),
  })
  expect(predicate({
    a : 'foo',
    b : 'bar',
    x : 11,
    y : 19,
  })).toEqual(false)
})

whereEq

whereEq<T, U>(condition: T, input: U): boolean

It will return true if all of input object fully or partially include rule object.

const condition = { a : { b : 1 } }
const input = {
  a : { b : 1 },
  c : 2
}

const result = whereEq(condition, input)
//=> true

Try the above R.whereEq example in Rambda REPL

All Typescript definitions
whereEq<T, U>(condition: T, input: U): boolean;
whereEq<T>(condition: T): <U>(input: U) => boolean;
Tests
import { whereEq } from './whereEq'

test('when true', () => {
  const condition = { a : 1 }
  const input = {
    a : 1,
    b : 2,
  }

  const result = whereEq(condition, input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const condition = { a : 1 }
  const input = { b : 2 }

  const result = whereEq(condition, input)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

test('with nested object', () => {
  const condition = { a : { b : 1 } }
  const input = {
    a : { b : 1 },
    c : 2,
  }

  const result = whereEq(condition)(input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('with wrong input', () => {
  const condition = { a : { b : 1 } }

  expect(() => whereEq(condition, null)).toThrowWithMessage(TypeError,
    'Cannot read property \'a\' of null')
})

without

without<T>(matchAgainst: ReadonlyArray<T>, source: ReadonlyArray<T>): T[]

It will return a new array, based on all members of source list that are not part of matchAgainst list.

const source = [1, 2, 3, 4]
const matchAgainst = [2, 3]

const result = R.without(matchAgainst, source)
// => [1, 4]

Try the above R.without example in Rambda REPL

All Typescript definitions
without<T>(matchAgainst: ReadonlyArray<T>, source: ReadonlyArray<T>): T[];
without<T>(matchAgainst: ReadonlyArray<T>): (source: ReadonlyArray<T>) => T[];
Tests
import { without } from './without'

test('should return a new list without values in the first argument ', () => {
  const itemsToOmit = [ 'A', 'B', 'C' ]
  const collection = [ 'A', 'B', 'C', 'D', 'E', 'F' ]

  expect(without(itemsToOmit, collection)).toEqual([ 'D', 'E', 'F' ])
  expect(without(itemsToOmit)(collection)).toEqual([ 'D', 'E', 'F' ])
})

test('ramda test', () => {
  expect(without([ 1, 2 ])([ 1, 2, 1, 3, 4 ])).toEqual([ 3, 4 ])
})

xor

xor(x: boolean, y: boolean): boolean
const result = [
  xor(true, true),
  xor(false, false),
  xor(false, true),
]
// => [false, false, true]

Try the above R.xor example in Rambda REPL

All Typescript definitions
xor(x: boolean, y: boolean): boolean;
xor(y: boolean): (y: boolean) => boolean;
Tests
import { xor } from './xor'

test('compares two values with exclusive or', () => {
  expect(xor(true, true)).toEqual(false)
  expect(xor(true, false)).toEqual(true)
  expect(xor(false, true)).toEqual(true)
  expect(xor(false, false)).toEqual(false)
})

test('when both values are truthy, it should return false', () => {
  expect(xor(true, 'foo')).toEqual(false)
  expect(xor(42, true)).toEqual(false)
  expect(xor('foo', 42)).toEqual(false)
  expect(xor({}, true)).toEqual(false)
  expect(xor(true, [])).toEqual(false)
  expect(xor([], {})).toEqual(false)
  expect(xor(new Date(), true)).toEqual(false)
  expect(xor(true, Infinity)).toEqual(false)
  expect(xor(Infinity, new Date())).toEqual(false)
})

test('when both values are falsy, it should return false', () => {
  expect(xor(null, false)).toEqual(false)
  expect(xor(false, undefined)).toEqual(false)
  expect(xor(undefined, null)).toEqual(false)
  expect(xor(0, false)).toEqual(false)
  expect(xor(false, NaN)).toEqual(false)
  expect(xor(NaN, 0)).toEqual(false)
  expect(xor('', false)).toEqual(false)
})

test('when one argument is truthy and the other is falsy, it should return true', () => {
  expect(xor('foo', null)).toEqual(true)
  expect(xor(null, 'foo')).toEqual(true)
  expect(xor(undefined, 42)).toEqual(true)
  expect(xor(42, undefined)).toEqual(true)
  expect(xor(Infinity, NaN)).toEqual(true)
  expect(xor(NaN, Infinity)).toEqual(true)
  expect(xor({}, '')).toEqual(true)
  expect(xor('', {})).toEqual(true)
  expect(xor(new Date(), 0)).toEqual(true)
  expect(xor(0, new Date())).toEqual(true)
  expect(xor([], null)).toEqual(true)
  expect(xor(undefined, [])).toEqual(true)
})

test.skip('returns a curried function', () => {
  expect(xor()(true)(true)).toEqual(false)
  expect(xor()(true)(false)).toEqual(true)
  expect(xor()(false)(true)).toEqual(true)
  expect(xor()(false)(false)).toEqual(false)
})

zip

zip<K, V>(x: ReadonlyArray<K>, y: ReadonlyArray<V>): KeyValuePair<K, V>[]

It will return a new array containing tuples of equally positions items from both x and y lists.

The returned list will be truncated to match the length of the shortest supplied list.

const x = [1, 2]
const y = ['A', 'B']
R.zip(x, y)
// => [[1, 'A'], [2, 'B']]

// truncates to shortest list
R.zip([...x, 3], ['A', 'B'])
// => [[1, 'A'], [2, 'B']]

Try the above R.zip example in Rambda REPL

All Typescript definitions
zip<K, V>(x: ReadonlyArray<K>, y: ReadonlyArray<V>): KeyValuePair<K, V>[];
zip<K>(x: ReadonlyArray<K>): <V>(y: ReadonlyArray<V>) => KeyValuePair<K, V>[];
Tests
import { zip } from './zip'

const array1 = [ 1, 2, 3 ]
const array2 = [ 'A', 'B', 'C' ]

test('should return an array', () => {
  const actual = zip(array1)(array2)
  expect(actual).toBeInstanceOf(Array)
})

test('should return and array or tuples', () => {
  const expected = [
    [ 1, 'A' ],
    [ 2, 'B' ],
    [ 3, 'C' ],
  ]
  const actual = zip(array1, array2)
  expect(actual).toEqual(expected)
})

test('should truncate result to length of shorted input list', () => {
  const expectedA = [
    [ 1, 'A' ],
    [ 2, 'B' ],
  ]
  const actualA = zip([ 1, 2 ], array2)
  expect(actualA).toEqual(expectedA)

  const expectedB = [
    [ 1, 'A' ],
    [ 2, 'B' ],
  ]
  const actualB = zip(array1, [ 'A', 'B' ])
  expect(actualB).toEqual(expectedB)
})

zipObj

zipObj<T>(keys: ReadonlyArray<string>, values: ReadonlyArray<T>): { [index: string]: T }

It will return a new object with keys of keys array and values of values array.

const keys = ['a', 'b', 'c']

R.zipObj(keys, [1, 2, 3])
//=> {a: 1, b: 2, c: 3}

// truncates to shortest list
R.zipObj(keys, [1, 2])
//=> {a: 1, b: 2}

Try the above R.zipObj example in Rambda REPL

All Typescript definitions
zipObj<T>(keys: ReadonlyArray<string>, values: ReadonlyArray<T>): { [index: string]: T };
zipObj(keys: ReadonlyArray<string>): <T>(values: ReadonlyArray<T>) => { [index: string]: T };

// RAMBDAX_MARKER_START
Tests
import { equals } from './equals'
import { zipObj } from './zipObj'

test('zipObj', () => {
  expect(zipObj([ 'a', 'b', 'c' ], [ 1, 2, 3 ])).toEqual({
    a : 1,
    b : 2,
    c : 3,
  })
})

test('0', () => {
  expect(zipObj([ 'a', 'b' ])([ 1, 2, 3 ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('1', () => {
  expect(zipObj([ 'a', 'b', 'c' ])([ 1, 2 ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('ignore extra keys', () => {
  const result = zipObj([ 'a', 'b', 'c', 'd', 'e', 'f' ], [ 1, 2, 3 ])
  const expected = {
    a : 1,
    b : 2,
    c : 3,
  }

  expect(equals(result, expected)).toBeTrue()
})

CHANGELOG

4.0.0

Deprecate the following methods:

  • R.promiseAllObject - because R.produce serves the same purpose
  • R.composed - because R.piped makes more sense, when we want to pass the input at the start of the function
  • R.defaultToStrict - confusing logic
  • R.findInObject - overestimated importance
  • R.headObject - overestimated importance
  • R.includesType - overestimated importance
  • R.inject - confusing logic
  • R.isAttach - confusing logic
  • R.mergeRight - overestimated importance
  • R.opposite - overestimated importance
  • R.otherwise - overestimated importance
  • R.pushUniq - overestimated importance
  • R.resolve - overestimated importance
  • R.s - overestimated importance
  • R.toggle - overestimated importance
  • R.uuid - not suitable
  • R.whenAsync - overestimated importance

Move the following methods to Rambda and change their logic to match Ramda implementation:

  • R.hasPath
  • R.unless
  • R.pathEq
  • R.tryCatch
  • R.where
  • R.whereEq

Also these changes:

  • R.ifElseAsync - accept any number of arguments for the returned function

  • R.produce, R.filterAsync, R.debounce, R.throttle - fix typings

  • R.mapAsyncLimit - drop support for curring and therefore for usage with R.composeAsync

  • Improve R.ok throwed error message

  • R.ok returns undefined instead of true when validation passes.

  • R.mergeDeep is renamed to R.mergeDeepLeft

  • Add R.pipeAsync

  • Take R.partialCurry from Rambda as it is deprecated there

3.7.0

Sync with Rambda

Add R.lens

Add R.lensIndex

Add R.lensPath

Add R.lensProp

Add R.over

Add R.set

Add R.view

Add R.paths

Add R.xor

Add R.cond

3.6.0

  • Add R.mapAsyncLimit

  • Add R.toggle, match Ramda upcoming method specification

  • Add R.isValidAsync

  • Extend R.template without introducing breaking change

3.5.0 Sync with Rambda - add methods descriptions to Typescript definitions

3.4.0 Sync with Rambda and close Issue #42

3.3.0 Fix R.sortObject typing

3.3.0 Add R.filterAsync and R.sortObject methods

3.2.0 R.uuid accept second argument in order to return string only uuid

3.1.0 Dynamic set of exports lead to adding previously ommited Rambda exports such as R.identical

3.0.3 Sync with Rambda - new functionality of R.isEmpty

3.0.2 Add typings for R.mapToObject

3.0.1 Fix typings

3.0.0 Breaking change as Rambda also has breaking changes

Read more about it in Rambda changelog

Also with this versions, typings tests are provided and several definitions are changed.

  • R.anyTrue, R.anyFalse, R.allTrue, R.allFalse use internal isTruthy and isFalsy methods. Empty array and object with zero length are considered falsy.

  • Deprecate R.contains

  • Deprecate R.defaultToWhen

  • Moved R.runTests to helpers repo

2.17.0 Change in R.runTests logic. It will be removed from Rambdax to helpers repo.

2.16.0 Restore R.runTests but without documentation

  • export getEvaluations, getPositiveEvaluation, getNegativeEvaluation in the context of R.runTests

2.15.0 Several changes

  • Typescript definitions have been updated and typings tests are introduced

  • R.mapAsync and R.mapFastAsync pass index as second argument

2.14.1 Restore R.contains

2.14.0 Several changes:

  • R.inject accept before flag as fourth argument

  • Remove R.includesAny

  • Improve typing of R.partition

  • R.nextIndex and R.prevIndex work also with number as second argument

2.13.1 Deprecate R.log and R.runTests

2.12.3 Add 'dist' directory to files

2.12.2 Add R.mapToObject typings

2.12.0 Sync with Rambda

2.11.1 Fix R.waitFor

2.11.0 Add R.toDecimal

2.10.2 Fix issue 32

2.10.0 deprecate R._

2.9.1 R.fromPairs/toPairs typing

2.9.0 npm doesn't update version on their site

2.8.2 R.map typing

2.8.0 Sync with Rambda | no need for create types script

2.7.0 Add R.prevIndex

2.6.2 Sync with Rambda

2.6.0 R.log depends on RAMBDAX_LOG

2.5.0 Rambda's partial

2.4.0 Add R.uuid

2.3.0 R._ parse to constant case

This introduce breaking change for ie11 as noted in issue 31 which is fixed with 2.10.0 which deprecates this method

2.2.1 Add R.log, R.logInit and R.logHolder

2.1.0 Add R._

2.0.0 Add R.toggle

1.9.0 Add R.pushUniq

1.8.2 No need for sourcemaps

1.8.1 Fix building with regeneratorRuntime

1.8.0 Upgrade to new major Rollup release

  • Restore R.headObject

  • Add R.hasPath method

1.7.2 R.memoize contains dev console.logs

1.7.1 Forgot to build types

1.7.0 Rename R.then to R.resolve because of Ramda issue with R.then(they rename it to R.andThen)

  • Add R.isFalsy, R.nextIndex and R.mergeDeep

1.6.3 Forgot to export R.unless(credit to @mobily for the PR)

1.6.0 Restore R.compact method

1.5.6 R.maybe accepts also anonymous functions as second and third argument

1.5.5 Add R.maybe method

  • Fix errors caugth by DeepScan service
  • Fix Typescript definitions for R.then and R.otherwise
  • R.change increase nesting level to 4

1.4.1 R.isValid didn't work with Number prototype

1.4.0 Add multiple methods

  • Add R.defaultToStrict

  • Add R.defaultToWhen

  • Add R.whereEq

  • Add R.partition

  • Add R.negate is renamed to R.opposite

  • Add R.then

  • Add R.otherwise

  • R.isValid accepts prototypes as rules, i.e. schema = {a: String}

  • The prevoious point leads to the same change applied to the methods depending on R.isValid, i.e. R.ok, R.pass and R.isAttach

    1.3.0 Add R.unless

  • R.when accepts both function and value for whenTrue argument. The same is valid for R.unless

  • export R.negate which is the same as R.complement

    1.2.0 Export src folder

    1.1.0 Restore promiseAllObject and flatMap

    1.0.1 Fix typings

    1.0.0 Deprecate the following methods:

  • compact

  • evolve

  • flatMap

  • greater

  • intersection

  • less

  • omitBy

  • pickBy

  • promiseAllObject

  • promiseAllSecure

  • rangeBy

Also pass deprecation of addIndex from Rambda@2.0.0

0.24.0 add R.pipedAsync, replace R.multiline with R.glue, remove R.validate

0.23.0 Add R.count

0.22.0 Add R.includesAny

0.21.0 Add R.includesType

0.20.1 R.pass and R.ok work with single schema.

0.20.0 Add R.pathEq

0.19.0 Add R.wait, expose already complete R.waitFor

0.18.0 AddR.anyType and R.allType

0.17.0 Rename R.is to R.pass and restore R.is original functionality.

0.16.0 getter, setter, reset methods

0.15.3 No more prepublish script

0.15.2 curry in remove

Last version with lib folder exposed

Additional info

Most influential contributors

Rambda references

Links to Rambda