array-map-to-object

Creates a new object with the returned keys and values of calling a provided function on every element in the calling array.

Usage no npm install needed!

<script type="module">
  import arrayMapToObject from 'https://cdn.skypack.dev/array-map-to-object';
</script>

README

array-map-to-object

Like map(), but creates object keys and values instead of array. mapToObject creates a new object with the returned keys and values of calling a provided function on every element in the calling array.

Published as .js, .mjs, umd.js including type definitions for TypeScript.

Syntax

const newObject = mapToObject(array, (currentValue[, index[, array]]) => {
  // Return key for object item
  // or [key, value] tuple (array) for key and value
  // or { key, value } object for key and value
}, [, thisArg]);

Examples

import mapToObject from "array-map-to-object";

Using a property for key to create object

const users = [{ name: "George", basketSize: 3 }, { name: "Lisa", basketSize: 2 }];
const usersLookup = mapToObject(users, user => user.name);
// Callback returns only key, value is same item. `usersLookup` is:
// { George: { name: "George", basketSize: 3 }, Lisa: { name: "Lisa", basketSize: 2 } }

Creating custom object using key/value pair.

const users = [{ name: "George", basketSize: 3 }, { name: "Lisa", basketSize: 2 }];
const usersLookup = mapToObject(users, user => [user.name, user.basketSize]);
// Callback returns [key, value] tuple (array). First returned value used for key, second for value. `usersLookup` is:
// { George: 3, Lisa: 2 }

Creating custom object using key/value object.

const users = [{ name: "George", basketSize: 3 }, { name: "Lisa", basketSize: 2 }];
const usersLookup = mapToObject(users, user => ({ key: user.name, value: user.basketSize }));
// Callback returns { key, value } object. `usersLookup` is:
// { George: 3, Lisa: 2 }

Mapping an array of numbers to an array of square roots

const numbers = [1, 4, 9];
const roots = mapToObject(numbers, num => [num, Math.sqrt(num)]);
// `roots` is { 1: 1, 4: 2, 9: 3 }

API

array-map-to-object

Index

Type aliases

Functions

Type aliases

Key

Ƭ Key: string | number | symbol

Defined in array-map-to-object.ts:4

Type of key used in created object.

KeyProducer

Ƭ KeyProducer: function

Defined in array-map-to-object.ts:13

Callback function that produces an element of the created object, which returns only single value used for key. Current array item is used as the value for the key in created object.

callback

Type declaration:

▸ (currentValue: T, index: number, array: T[]): K

Parameters:

Name Type Description
currentValue T is the current element being processed in the array.
index number is the index of the current element being processed in the array.
array T[] is the array map was called upon.

KeyValueProducer

Ƭ KeyValueProducer: function

Defined in array-map-to-object.ts:29

Callback function that produces an element of the created object, which returns values used for key and value in created object.

callback

Type declaration:

▸ (currentValue: T, index: number, array: T[]): [K, V] | object

Parameters:

Name Type Description
currentValue T is the current element being processed in the array.
index number is the index of the current element being processed in the array.
array T[] is the array map was called upon.

Functions

mapToObject

▸ mapToObject<T, K, V>(array: T[], callback: KeyValueProducer‹T, K, V›, thisArg?: any): Record<K, V>

Defined in array-map-to-object.ts:58

Creates a new object with the results of calling a provided function on every element in the calling array. Returned key and value is added to created object.

mapToObject calls a provided callback function once for each element in an array, in order, and constructs a new object from the results. callback is invoked only for indexes of the array which have assigned values, including undefined. It is not called for missing elements of the array (that is, indexes that have never been set, which have been deleted or which have never been assigned a value).#### Example

const array = ["Red", "Green"];
mapToObject(array, (currentValue) => [currentValue.toUpperCase(), currentValue.toLowerCase()]); // { "RED": "red", "GREEN": "green" }
mapToObject(array, (currentValue) => { key: currentValue.toUpperCase(), value: currentValue.toLowerCase() }); // { "RED": "red", "GREEN": "green" }

Type parameters:

▪ T

is array elements.

▪ K: Key

is keys of returned object.

▪ V

is values of returned object.

Parameters:

Name Type
array T[]
callback KeyValueProducer‹T, K, V›
thisArg? any

Returns: Record<K, V>

▸ mapToObject<T, K>(array: T[], callback: KeyProducer‹T, K›, thisArg?: any): Record<K, T>

Defined in array-map-to-object.ts:72

Creates a new object with the results of calling a provided function on every element in the calling array. Returned key and current array item (as value) is added to created object.

mapToObject calls a provided callback function once for each element in an array, in order, and constructs a new object from the results. callback is invoked only for indexes of the array which have assigned values, including undefined. It is not called for missing elements of the array (that is, indexes that have never been set, which have been deleted or which have never been assigned a value).#### Example

const array = ["Red", "Green"];
mapToObject(array, (currentValue) => currentValue.toUpperCase()); // { "RED": "Red", "GREEN": "Green" }

Type parameters:

▪ T

is array elements.

▪ K: Key

is keys of returned object.

Parameters:

Name Type
array T[]
callback KeyProducer‹T, K›
thisArg? any

Returns: Record<K, T>