Package Exports

typelevel-ts

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 (typelevel-ts) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

TypeScript compatibility

The stable version is tested against TypeScript 2.9.1+

API

Equals<A, B>

Returns the string literal 'T' if A and B are equal types, 'F' otherwise

Equals<string, string> // "T"
Equals<string, number> // "F"

Omit<A extends object, K extends string | number | symbol>

Extracts a super-type of A identified by its keys K

Omit<{ a: string; b: number }, 'a'> // { b: number }

Overwrite<A extends object, B extends object>

Overwrite<{ a: string; b: number }, { b: boolean }> // { a: string; b: boolean }

Diff<A extends object, K extends keyof A>

Diff<{ a: string; b: number }, 'b'> // { a: string; b?: number }

RowLacks<A extends object, K extends string | number | symbol>

Encodes the constraint that a given object A does not contain specific keys K

declare function f(x: RowLacks<{ a: string; b: number }, 'a'>): void
// $ExpectError
f({ a: 'foo', b: 1 })

Exact<A extends object, B extends A>

declare function f<T extends Exact<{ a: string }, T>>(a: T): void
declare const x: { a: string }
declare const y: { a: string; b: number }
f(x)
// $ExpectError
f(y)

KeysOfType<A extends object, B>

Picks only the keys of a certain type

KeysOfType<{a: string, b: string | boolean, c: boolean, d: string}, string> // "a" | "d"

AnyTuple

declare function f<T extends AnyTuple>(x: T): T
declare const x: [number]
declare const y: [number, string]
declare const z: [number, string, boolean]
declare const t: Array<number>
f(x)
f(y)
f(z)
// $ExpectError
f(t)

DeepReadonly

interface Foo {
  bar: {
    baz: string
    quux: Array<{ barbaz: number }>
  }
}

type ReadonlyFoo = DeepReadonly<Foo>
declare const x: ReadonlyFoo
// $ExpectError
x.bar.quux[1].barbaz = 1

TaggedUnionMember<A extends object, Tag extends keyof A, Value extends A[Tag]>

Extracts the type of a member of a tagged union

type A = { tag: 'A'; a: string }
type B = { tag: 'B'; b: number }
type C = A | B
TaggedUnionMember<C, 'tag', 'A'> // A

RequiredKeys and OptionalKeys

Extracts required or optional keys as a literal type union

type A = { a: string; b: number; x?: string; y?: number }
RequiredKeys<A> // "a" | "b"
OptionalKeys<A> // "x" | "y"