Object.fromEntries() - JavaScript 编辑

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

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The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Syntax

Object.fromEntries(iterable);

Parameters

iterable

An iterable such as Array or Map or other objects implementing the iterable protocol.

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, that returns an iterator object, that produces a two element array-like object, whose first element is a value that will be used as a property key, and whose second element is the value to associate with that property key.

Object.fromEntries() performs the reverse of Object.entries().

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 }

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Specifications

Specification
ECMAScript (ECMA-262) The definition of 'Object.fromEntries' in that specification.

Browser compatibility

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See also

• Object.entries()
• Object.keys()
• Object.values()
• Map.prototype.entries()
• Map.prototype.keys()
• Map.prototype.values()