object-setprototypeof-function-javascript.md

title	ms.custom	ms.date	ms.prod	ms.reviewer	ms.suite	ms.technology	ms.tgt_pltfrm	ms.topic	dev_langs	ms.assetid	caps.latest.revision	author	ms.author	manager
Object.setPrototypeOf Function (JavaScript) | Microsoft Docs		01/18/2017	windows-client-threshold			devlang-javascript		language-reference	JavaScript TypeScript DHTML	a2609f6e-aeee-4c13-b7cf-c31ddf58ff35	3	mikejo5000	mikejo	ghogen

Object.setPrototypeOf Function (JavaScript)

Sets the prototype of an object.

Syntax

Object.setPrototypeOf(obj, proto);  

Parameters

obj
Required. The object for which you are setting the prototype.

proto
Required. The new prototype object.

Remarks

Warning

Setting the prototype may reduce performance on all JavaScript code that has access to an object whose prototype has been mutated.

Example

The following code example shows how to set the prototype for an object.

function Rectangle() {  
}  
  
var rec = new Rectangle();  
  
if (console && console.log) {  
    console.log(Object.setPrototypeOf(rec) === Rectangle.prototype);  // Returns true  
    Object.getPrototypeOf(rec, Object.prototype);  
    console.log(Object.setPrototypeOf(rec) === Rectangle.prototype);  // Returns false  
}  

Example

The following code example shows how to add properties to an object by adding them to the prototype.

var proto = { y: 2 };  
  
var obj = { x: 10 };  
Object.setPrototypeOf(obj, proto);  
  
proto.y = 20;  
proto.z = 40;  
  
if (console && console.log) {  
    console.log(obj.x === 10);  // Returns true  
    console.log(obj.y === 20);  // Returns true  
    console.log(obj.z === 40);  // Returns true  
}  

Example

The following code example adds properties to the String object by setting a new prototype on it.

var stringProp = { desc: "description" };  
  
Object.setPrototypeOf(String, stringProp);  
var s1 = "333";  
var s2 = new String("333");  
  
if (console && console.log) {  
  
    console.log(String.desc === "description"); // Returns true  
    console.log(s1.desc === "description");     // Returns false  
    console.log(s2.desc === "description");     // Returns false  
  
    Object.setPrototypeOf(s1, String); // Can't be set.  
    Object.setPrototypeOf(s2, String);  
  
    console.log(s1.desc === "description"); // Returns false  
    console.log(s2.desc === "description"); // Returns true  
}  

Requirements

[!INCLUDEjsv12]