Object.entries() - JavaScript 编辑

The Object.entries() method returns an array of a given object's own enumerable string-keyed property [key, value] pairs, in the same order as that provided by a for...in loop. (The only important difference is that a for...in loop enumerates properties in the prototype chain as well). 

The order of the array returned by Object.entries() does not depend on how an object is defined. If there is a need for certain ordering, then the array should be sorted first, like Object.entries(obj).sort((a, b) => b[0].localeCompare(a[0]));.

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.entries(obj)

Parameters

obj

The object whose own enumerable string-keyed property [key, value] pairs are to be returned.

Return value

An array of the given object's own enumerable string-keyed property [key, value] pairs.

Description

Object.entries() returns an array whose elements are arrays corresponding to the enumerable string-keyed property [key, value] pairs found directly upon object. The ordering of the properties is the same as that given by looping over the property values of the object manually.

Polyfill

To add compatible Object.entries() support in older environments that do not natively support it, you can use any of the following:

• a demonstration implementation of Object.entries in the tc39/proposal-object-values-entries (if you don't need any support for IE);
• a polyfill in the es-shims/Object.entries repositories;
• or, you can use the simple, ready-to-deploy polyfill listed below:

if (!Object.entries) {
  Object.entries = function( obj ){
    var ownProps = Object.keys( obj ),
        i = ownProps.length,
        resArray = new Array(i); // preallocate the Array
    while (i--)
      resArray[i] = [ownProps[i], obj[ownProps[i]]];

    return resArray;
  };
}

For the above polyfill code snippet, if you need support for IE<9, then you will also need an Object.keys() polyfill (such as the one found on the Object.keys page).

Examples

const obj = { foo: 'bar', baz: 42 };
console.log(Object.entries(obj)); // [ ['foo', 'bar'], ['baz', 42] ]

// array like object
const obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.entries(obj)); // [ ['0', 'a'], ['1', 'b'], ['2', 'c'] ]

// array like object with random key ordering
const anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.entries(anObj)); // [ ['2', 'b'], ['7', 'c'], ['100', 'a'] ]

// getFoo is property which isn't enumerable
const myObj = Object.create({}, { getFoo: { value() { return this.foo; } } });
myObj.foo = 'bar';
console.log(Object.entries(myObj)); // [ ['foo', 'bar'] ]

// non-object argument will be coerced to an object
console.log(Object.entries('foo')); // [ ['0', 'f'], ['1', 'o'], ['2', 'o'] ]

// returns an empty array for any primitive type except for strings (see the above example), since primitives have no own properties
console.log(Object.entries(100)); // [ ]

// iterate through key-value gracefully
const obj = { a: 5, b: 7, c: 9 };
for (const [key, value] of Object.entries(obj)) {
  console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
}

// Or, using array extras
Object.entries(obj).forEach(([key, value]) => {
  console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
});

Converting an Object to a Map

The new Map() constructor accepts an iterable of entries. With Object.entries, you can easily convert from Object to Map:

const obj = { foo: 'bar', baz: 42 };
const map = new Map(Object.entries(obj));
console.log(map); // Map(2) {"foo" => "bar", "baz" => 42}

Iterating through an Object

Using Array Destructuring, you can iterate through objects easily.

const obj = { foo: 'bar', baz: 42 };
Object.entries(obj).forEach(([key, value]) => console.log(`${key}: ${value}`)); // "foo: bar", "baz: 42"

Specifications

Browser compatibility

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See also

• Enumerability and ownership of properties
• Object.keys()
• Object.values()
• Object.prototype.propertyIsEnumerable()
• Object.create()
• Object.fromEntries()
• Object.getOwnPropertyNames()
• Map.prototype.entries()
• Map.prototype.keys()
• Map.prototype.values()