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The Object.keys() method returns an array of a given object's property names, in the same order as we get with a normal loop.

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

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

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

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

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

If you want all properties, even non-enumerables, see Object.getOwnPropertyNames().

Notes

In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError. In ES2015, a non-object argument will be coerced to an object.

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

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

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 Status Comment
ECMAScript 5.1 (ECMA-262)
The definition of 'Object.keys' in that specification.
Standard Initial definition. Implemented in JavaScript 1.8.5.
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Object.keys' in that specification.
Standard  
ECMAScript Latest Draft (ECMA-262)
The definition of 'Object.keys' in that specification.
Draft  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support5 Yes49125
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support Yes Yes Yes4 Yes Yes Yes

See also