Returns a reference to the Object constructor function that created the instance object. Note that the value of this property is a reference to the function itself, not a string containing the function's name. The value is only read-only for primitive values such as 1true and "test".

Description

All objects will have a constructor property.  Objects created without the explicit use of a constructor function (i.e. the object and array literals) will have a constructor property that points to the Fundamental Object constructor type for that object.

var o = {};
o.constructor === Object; // true

var o = new Object;
o.constructor === Object; // true

var a = [];
a.constructor === Array; // true

var a = new Array;
a.constructor === Array // true

var n = new Number(3);
n.constructor === Number; // true

Examples

Displaying the constructor of an object

The following example creates a prototype, Tree, and an object of that type, theTree. The example then displays the constructor property for the object theTree.

function Tree(name) {
  this.name = name;
}

var theTree = new Tree('Redwood');
console.log('theTree.constructor is ' + theTree.constructor);

This example displays the following output:

theTree.constructor is function Tree(name) {
  this.name = name;
}

Changing the constructor of an object

The following example shows how to modify constructor value of generic objects. Only true, 1 and "test" will not be affected as they have read-only native constructors. This example shows that it is not always safe to rely on the constructor property of an object.

function Type () {}

var types = [
  new Array(),
  [],
  new Boolean(),
  true,             // remains unchanged
  new Date(),
  new Error(),
  new Function(),
  function () {},
  Math,
  new Number(),
  1,                // remains unchanged
  new Object(),
  {},
  new RegExp(),
  /(?:)/,
  new String(),
  'test'            // remains unchanged
];

for (var i = 0; i < types.length; i++) {
  types[i].constructor = Type;
  types[i] = [types[i].constructor, types[i] instanceof Type, types[i].toString()];
}

console.log(types.join('\n'));

This example displays the following output:

function Type() {},false,
function Type() {},false,
function Type() {},false,false
function Boolean() {
    [native code]
},false,true
function Type() {},false,Mon Sep 01 2014 16:03:49 GMT+0600
function Type() {},false,Error
function Type() {},false,function anonymous() {

}
function Type() {},false,function () {}
function Type() {},false,[object Math]
function Type() {},false,0
function Number() {
    [native code]
},false,1
function Type() {},false,[object Object]
function Type() {},false,[object Object]
function Type() {},false,/(?:)/
function Type() {},false,/(?:)/
function Type() {},false,
function String() {
    [native code]
},false,test

Specifications

Specification Status Comment
ECMAScript 1st Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.1.
ECMAScript 5.1 (ECMA-262)
The definition of 'Object.prototype.constructor' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Object.prototype.constructor' in that specification.
Standard  
ECMAScript Latest Draft (ECMA-262)
The definition of 'Object.prototype.constructor' in that specification.
Living Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support Yes Yes Yes Yes Yes Yes
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support Yes Yes Yes Yes Yes Yes Yes

Document Tags and Contributors

 Last updated by: Congelli501,