map-obj

Map object keys and values into a new object

Install

npm install map-obj

Usage

import mapObject, {mapObjectSkip} from 'map-obj';

// Swap keys and values
const newObject = mapObject({foo: 'bar'}, (key, value) => [value, key]);
//=> {bar: 'foo'}

// Convert keys to lowercase (shallow)
const newObject = mapObject({FOO: true, bAr: {bAz: true}}, (key, value) => [key.toLowerCase(), value]);
//=> {foo: true, bar: {bAz: true}}

// Convert keys to lowercase (deep recursion)
const newObject = mapObject({FOO: true, bAr: {bAz: true}}, (key, value) => [key.toLowerCase(), value], {deep: true});
//=> {foo: true, bar: {baz: true}}

// Filter out specific values
const newObject = mapObject({one: 1, two: 2}, (key, value) => value === 1 ? [key, value] : mapObjectSkip);
//=> {one: 1}

// Include symbol keys
const symbol = Symbol('foo');
const newObject = mapObject({bar: 'baz', [symbol]: 'qux'}, (key, value) => [key, value], {includeSymbols: true});
//=> {bar: 'baz', [Symbol(foo)]: 'qux'}

API

mapObject(source, mapper, options?)

source

Type: object

The source object to copy properties from.

mapper

Type: (sourceKey, sourceValue, source) => [targetKey, targetValue, mapperOptions?] | mapObjectSkip

A mapping function.

[!NOTE] When options.deep is true, the mapper receives keys and values from nested objects and arrays. The sourceKey parameter is typed as string | symbol and sourceValue as unknown to reflect the actual runtime behavior when recursing into unknown shapes. The third argument source is always the original input object, not the current nested owner.

mapperOptions

Type: object

shouldRecurse

Type: boolean
Default: true

Whether to recurse into targetValue.

Requires deep: true.

options

Type: object

deep

Type: boolean
Default: false

Recurse nested objects and objects in arrays.

Built-in objects like RegExp, Error, Date, Map, Set, WeakMap, WeakSet, Promise, ArrayBuffer, DataView, typed arrays (Uint8Array, etc.), and Blob are not recursed into. Special objects like Jest matchers are also automatically excluded.

includeSymbols

Type: boolean
Default: false

Include symbol keys in the iteration.

By default, symbol keys are completely ignored and not passed to the mapper function. When enabled, the mapper will also be called with symbol keys from the source object, allowing them to be transformed or included in the result. Only enumerable symbol properties are included.

target

Type: object
Default: {}

The target object to map properties onto.

mapObjectSkip

Return this value from a mapper function to exclude the key from the new object.

import mapObject, {mapObjectSkip} from 'map-obj';

const object = {one: 1, two: 2};
const mapper = (key, value) => value === 1 ? [key, value] : mapObjectSkip;
const result = mapObject(object, mapper);

console.log(result);
//=> {one: 1}

Related

• filter-obj - Filter object keys and values into a new object