Object.setPrototypeOf()

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句法
描述
Appending Prototype Chains
Polyfill
范例
规范
浏览器兼容性
另请参阅
相关话题

Object.setPrototypeOf() method sets the prototype (i.e., the internal [[Prototype]] property) of a specified object to another object or null .

警告： Changing the [[Prototype]] of an object is, by the nature of how modern JavaScript engines optimize property accesses , currently a very slow operation in every browser and JavaScript engine. In addition, the effects of altering inheritance are subtle and far-flung, and are not limited to simply the time spent in the Object.setPrototypeOf(...) statement, but may extend to any code that has access to any object whose [[Prototype]] has been altered.

Because this feature is a part of the language, it is still the burden on engine developers to implement that feature performantly (ideally). Until engine developers address this issue, if you are concerned about performance, you should avoid setting the [[Prototype]] of an object. Instead, create a new object with the desired [[Prototype]] 使用 Object.create() .

句法

Object.setPrototypeOf(obj, prototype)

参数

obj
prototype: The object's new prototype (an object or null ).

返回值

The specified object.

描述

抛出 TypeError exception if the object whose [[Prototype]] is to be modified is non-extensible according to Object.isExtensible() . Does nothing if the prototype parameter isn't an object or null (i.e., number, string, boolean, or undefined ). Otherwise, this method changes the [[Prototype]] of obj to the new value.

Object.setPrototypeOf() is in the ECMAScript 2015 specification. It is generally considered the proper way to set the prototype of an object, vs. the more controversial Object.prototype.__proto__ 特性。

Appending Prototype Chains

A combination of Object.getPrototypeOf() and Object.prototype.__proto__ permits appending a whole prototype chain to a new prototype object:

/**
*** Object.appendChain(@object, @prototype)
*
* Appends the first non-native prototype of a chain to a new prototype.
* Returns @object (if it was a primitive value it will transformed into an object).
*
*** Object.appendChain(@object [, "@arg_name_1", "@arg_name_2", "@arg_name_3", "..."], "@function_body")
*** Object.appendChain(@object [, "@arg_name_1, @arg_name_2, @arg_name_3, ..."], "@function_body")
*
* Appends the first non-native prototype of a chain to the native Function.prototype object, then appends a
* new Function(["@arg"(s)], "@function_body") to that chain.
* Returns the function.
*
**/
Object.appendChain = function(oChain, oProto) {
  if (arguments.length < 2) {
    throw new TypeError('Object.appendChain - Not enough arguments');
  }
  if (typeof oProto !== 'object' && typeof oProto !== 'string') {
    throw new TypeError('second argument to Object.appendChain must be an object or a string');
  }
  var oNewProto = oProto,
      oReturn = o2nd = oLast = oChain instanceof this ? oChain : new oChain.constructor(oChain);
  for (var o1st = this.getPrototypeOf(o2nd);
    o1st !== Object.prototype && o1st !== Function.prototype;
    o1st = this.getPrototypeOf(o2nd)
  ) {
    o2nd = o1st;
  }
  if (oProto.constructor === String) {
    oNewProto = Function.prototype;
    oReturn = Function.apply(null, Array.prototype.slice.call(arguments, 1));
    this.setPrototypeOf(oReturn, oLast);
  }
  this.setPrototypeOf(o2nd, oNewProto);
  return oReturn;
}

用法

First example: Appending a chain to a prototype

function Mammal() {
  this.isMammal = 'yes';
}
function MammalSpecies(sMammalSpecies) {
  this.species = sMammalSpecies;
}
MammalSpecies.prototype = new Mammal();
MammalSpecies.prototype.constructor = MammalSpecies;
var oCat = new MammalSpecies('Felis');
console.log(oCat.isMammal); // 'yes'
function Animal() {
  this.breathing = 'yes';
}
Object.appendChain(oCat, new Animal());
console.log(oCat.breathing); // 'yes'

Second example: Transforming a primitive value into an instance of its constructor and append its chain to a prototype

function MySymbol() {
  this.isSymbol = 'yes';
}
var nPrime = 17;
console.log(typeof nPrime); // 'number'
var oPrime = Object.appendChain(nPrime, new MySymbol());
console.log(oPrime); // '17'
console.log(oPrime.isSymbol); // 'yes'
console.log(typeof oPrime); // 'object'

Third example: Appending a chain to the Function.prototype object and appending a new function to that chain

function Person(sName) {
  this.identity = sName;
}
var george = Object.appendChain(new Person('George'),
                                'console.log("Hello guys!!");');
console.log(george.identity); // 'George'
george(); // 'Hello guys!!'

Polyfill

Using the older Object.prototype.__proto__ property, we can easily define Object.setPrototypeOf if it isn't available already:

if (!Object.setPrototypeOf) {
    // Only works in Chrome and FireFox, does not work in IE:
     Object.prototype.setPrototypeOf = function(obj, proto) {
         if(obj.__proto__) {
             obj.__proto__ = proto;
             return obj;
         } else {
             // If you want to return prototype of Object.create(null):
             var Fn = function() {
                 for (var key in obj) {
                     Object.defineProperty(this, key, {
                         value: obj[key],
                     });
                 }
             };
             Fn.prototype = proto;
             return new Fn();
         }
     }
}

范例

Using Object.setPrototypeOf

var dict = Object.setPrototypeOf({}, null);

规范

规范
ECMAScript (ECMA-262) The definition of 'Object.setPrototypeOf' in that specification.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`setPrototypeOf`	Chrome 34	Edge 12	Firefox 31	IE 11	Opera 21	Safari 9	WebView Android 37	Chrome Android 34	Firefox Android 31	Opera Android 21	Safari iOS 9	Samsung Internet Android 2.0	nodejs 0.12

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句法

参数

返回值

描述