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
Supported in Microsoft Edge (Edge browser). Also supported in Store apps (Microsoft Edge on Windows 10). See Version Information.
Not supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards, Internet Explorer 11 standards. Not supported in Windows 8.1.

