当其构造函数的原型不是对象时，如何创建对象？ [英] How objects are created when the prototype of their constructor isn't an object?

问题描述

我回答了这个问题：如何创建对象？
，但回答完之后我还有一个问题。

I answered this question: How do objects created? but I also have a question after I answered it.

function Bar() {
    this.foo = true;
}
console.log('obj3');
Bar.prototype = 3;
var obj3 = new Bar();
console.log(obj3);
console.log(obj3.constructor === Bar);
console.log(obj3.constructor === Object);
  
console.log(Object.prototype === Object.getPrototypeOf(obj3));
console.log(obj3.foo);

Bar.prototype = 3 ，我的理论是，当 new Bar（）执行，如步骤2 所示，应该将创建的对象链接到 Bar.prototype ，但是由于 Bar.prototype 不引用对象，暗含了默认值，即 Object.prototype 。

Bar.prototype = 3, my theory is that, when new Bar() executed, as in Step 2, the created object is supposed to linked to Bar.prototype, but since the value of Bar.prototype doesn't refer to an object, implicitly a default value was assigned, which is the Object.prototype.

由于 object.prototype.constructor 对 Object ， obj3.constructor 也引用 Object ，但 obj3 第1步，code>的事实构造函数仍为 Bar 由 console.log（obj3.foo）证明； //正确。

Due to object.prototype.constructor's reference to the Object, obj3.constructor also refer to the Object, but obj3's de facto constructor is still Bar, because of Step 1, which also can be proved by console.log(obj3.foo); // true.

是吗？

@Leo问我是否可以提供有关内部机制的更多信息。他已经在Firefox Chrome Safari中对其进行了测试，它们的行为都相同，他认为这应该在ECMA-262中明确规定。但是，他来对地方了。但是我也没有找到任何证据可以支持我的论点，因此，我正在寻求您的帮助。您能否提供有关内部机制的更多信息？

@Leo asked me if I could provide more information about the internal mechanism. He had tested it in Firefox Chrome Safari, they all behave the same, he thinks it should be something clearly specified in ECMA-262. However, he hasn't got to the right place. But I didn't find anything to support my argument too, therefore I'm looking for your help. Could you provide more information about the internal mechanism?

推荐答案

是的，这是在 GetPrototypeFromConstructor ：

1. 让 proto 是？ 获取（构造函数，原型 ）。



2. 如果类型（ proto ）不是对象，那么

1. Let proto be ? Get(constructor, "prototype").

2. If Type(proto) is not Object, then

1. 让境界为？ GetFunctionRealm （ constructor ）


2. 让 proto 为领域的内部对象，名为 intrinsicDefaultProto 。

1. Let realm be ? GetFunctionRealm(constructor).
2. Let proto be realm's intrinsic object named intrinsicDefaultProto.

>

具体来说，它是这样的：

Specifically, it works like this:

1. new Bar（）调用 Bar。 [[Construct]]


2. 初始化 thisArgument 使用
   
   OrdinaryCreateFromConstructor （ newTarget ，％ObjectPrototype％ ）


3. 转动从
   
   继承的对象 GetPrototypeFromConstructor （构造函数， intrinsicDefaultProto ）

1. new Bar() calls Bar.[[Construct]]
2. That initializes the thisArgument using
   OrdinaryCreateFromConstructor(newTarget, "%ObjectPrototype%")
3. That returns an object which inherits from
   GetPrototypeFromConstructor(constructor, intrinsicDefaultProto)

因此，如果 prototype 不是对象，默认值为该领域的％ObjectPrototype％。

So if the prototypeis not an object, the default will be the %ObjectPrototype% of that realm.

请注意，并非总是 Object.prototype ：

var iframe = document.createElement('iframe');
document.body.appendChild(iframe);
var win = iframe.contentWindow;
document.body.removeChild(iframe);
var F = win.Function("")
F.prototype = 5;
var proto = Object.getPrototypeOf(new F());
proto === Object.prototype; // false
proto === win.Object.prototype; // true

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