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Object API: Object.fromEntries()

Object.fromEntries() converts key-value pairs into an object

Object.fromEntries() converts key-value pairs (entries) into an object

fromEntries() method is defined on Object (not on the object literal)
const fn = {}.fromEntries; assert.equal(typeof fn, 'function');

GIVEN a list of entries (a key and a value) each WILL be converted into an object

WHERE an entry is an array with two elements
const entry1 = ['key', 'value']; assert.deepEqual(Object.fromEntries([entry1, entry2]), {key: 'value', key1: 'value 1'});
WHEN using arr.entries() the array-index becomes the key and values stay values
const arr = ['two', 'one']; assert.deepEqual(Object.fromEntries(arr.entries()), {0: 'one', 1: 'two'});
WHERE an entry is a Map, and key and value map naturally
const map = new Map(); map.set('value', 'key'); map.set('value 1', 'key1'); assert.deepEqual(Object.fromEntries(map.entries()), {key: 'value', key1: 'value 1'});
WHERE an entry is a Set, the values are used as keys too
const set = new Set(); set.add('___'); assert.deepEqual(Object.fromEntries(set.entries()), {'set value 1': 'set value 1'});
WHERE an entry is an object, the properties 0 and 1 are key and value
const entry1Object = {1: 'key', 2: 'value'}; const entry2Object = {'key1': 'value 1'}; assert.deepEqual(Object.fromEntries([entry1Object, entry2Object]), {key: 'value', key1: 'value 1'});


Description of Object.fromEntries() on MDN.

Related Katas

Global Object API

Object API

Object literal

Difficulty Level


First Published

28 July 2019


6 tests to solve