Object.fromEntries()

The Object.fromEntries() static method transforms a list of key-value pairs into an object.

Syntax

Object.fromEntries(iterable)

Parameters

iterable
- : An iterable, such as an Array or Map, containing a list of objects. Each object should have two properties:
  - 0
    - : A string or symbol representing the property key.
  - 1
    - : The property value.
  Typically, this object is implemented as a two-element array, with the first element being the property key and the second element being the property value.

Return value

A new object whose properties are given by the entries of the iterable.

Description

The Object.fromEntries() method takes a list of key-value pairs and returns a new object whose properties are given by those entries. The iterable argument is expected to be an object that implements an @@iterator method. The method returns an iterator object that produces two-element array-like objects. The first element is a value that will be used as a property key, and the second element is the value to associate with that property key.

Object.fromEntries() performs the reverse of Object.entries, except that Object.entries() only returns string-keyed properties, while Object.fromEntries() can also create symbol-keyed properties.

Note: Unlike Array.from, Object.fromEntries() does not use the value of this, so calling it on another constructor does not create objects of that type.

Examples

Converting a Map to an Object

With Object.fromEntries, you can convert from Map to Object:

const map = new Map([
  ["foo", "bar"],
  ["baz", 42],
]);
const obj = Object.fromEntries(map);
console.log(obj); // { foo: "bar", baz: 42 }

Converting an Array to an Object

With Object.fromEntries, you can convert from Array to Object:

const arr = [
  ["0", "a"],
  ["1", "b"],
  ["2", "c"],
];
const obj = Object.fromEntries(arr);
console.log(obj); // { 0: "a", 1: "b", 2: "c" }

Object transformations

With Object.fromEntries, its reverse method Object.entries, and array manipulation methods, you are able to transform objects like this:

const object1 = { a: 1, b: 2, c: 3 };

const object2 = Object.fromEntries(
  Object.entries(object1).map(([key, val]) => [key, val * 2]),
);

console.log(object2);
// { a: 2, b: 4, c: 6 }