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 1
, true
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. |
Draft |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Edge | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |