Web/JavaScript/Reference/Global objects/Object/keys

The Object.keys() method returns an array of a given object's own enumerable property names, iterated in the same order that a normal loop would.

Syntax

Object.keys(obj)

Parameters

obj: The object of which the enumerable's own properties are to be returned.

Return value

An array of strings that represent all the enumerable properties of the given object.

Description

Object.keys() returns an array whose elements are strings corresponding to the enumerable properties found directly upon object. The ordering of the properties is the same as that given by looping over the properties of the object manually.

Examples

Using Object.keys

// simple array
const arr = ['a', 'b', 'c'];
console.log(Object.keys(arr)); // console: ['0', '1', '2']

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

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

// getFoo is a property which isn't enumerable
const myObj = Object.create({}, {
  getFoo: {
    value: function () { return this.foo; }
  } 
});
myObj.foo = 1;
console.log(Object.keys(myObj)); // console: ['foo']

If you want all properties—including non-enumerables—see Object.getOwnPropertyNames().

Non-object coercion

In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError.

From ES2015 onwards, a non-object argument will be coerced to an object.

// In ES5
Object.keys('foo');  // TypeError: "foo" is not an object 

// In ES2015+
Object.keys('foo');  // ["0", "1", "2"]

Polyfill

To add compatible Object.keys support in older environments that do not natively support it, copy the following snippet:

// From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
if (!Object.keys) {
  Object.keys = (function() {
    'use strict';
    var hasOwnProperty = Object.prototype.hasOwnProperty,
        hasDontEnumBug = !({ toString: null }).propertyIsEnumerable('toString'),
        dontEnums = [
          'toString',
          'toLocaleString',
          'valueOf',
          'hasOwnProperty',
          'isPrototypeOf',
          'propertyIsEnumerable',
          'constructor'
        ],
        dontEnumsLength = dontEnums.length;

    return function(obj) {
      if (typeof obj !== 'function' && (typeof obj !== 'object' || obj === null)) {
        throw new TypeError('Object.keys called on non-object');
      }

      var result = [], prop, i;

      for (prop in obj) {
        if (hasOwnProperty.call(obj, prop)) {
          result.push(prop);
        }
      }

      if (hasDontEnumBug) {
        for (i = 0; i < dontEnumsLength; i++) {
          if (hasOwnProperty.call(obj, dontEnums[i])) {
            result.push(dontEnums[i]);
          }
        }
      }
      return result;
    };
  }());
}

Please note that the above code includes non-enumerable keys in IE7 (and maybe IE8), when passing in an object from a different window.

For a simple Browser Polyfill, see Javascript - Object.keys Browser Compatibility.

Specifications

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

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`keys`	Chrome Full support 5	Edge Full support 12	Firefox Full support 4	IE Full support 9	Opera Full support 12	Safari Full support 5	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 12	Safari iOS Full support 5	Samsung Internet Android Full support 1.0	nodejs Full support Yes

Legend

Full support: Full support