Javascript原型链和原型的一个误区

之前我对Javascript的原型链中, 原型继承与标识符查找有些迷惑,

如, 如下的代码:

function Foo() {};

var foo = new Foo();

Foo.prototype.label = "laruence";

alert(foo.label); //output: laruence

alert(Foo.label);//output: undefined

今天看到了如下这个图:

Javascript object layout
另外, 在Javascript Object Hierarchy看到:

The prototype is only used for properties inherited by objects/instances created by that function. The function itself does not use the associated prototype.

也就是说, 函数对象的prototype并不作用于原型链查找过程中,

今天在firefox下发现(因为firefox通过__proto__暴露了[[prototype]]), 真正参与标识符查找的是函数对象的__proto__,

function Foo() {};

var foo = new Foo();

Foo.__proto__.label = "laruence";

alert(Foo.label); //output: laruence

alert(foo.label);//output: undefined

而, 显然的:

function Foo() {};

alert(Foo.__proto__ === Foo.prototype); //output: false

另外, 也解释了,

alert(Object.forEach); // undefined

 

Function.prototype.forEach = function(object, block, context) {

    for (var key in object) {

        if (typeof this.prototype[key] == "undefined") {

            block.call(context, object[key], key, object);

        }

    }

 

};

 

alert(Object.forEach);

alert(Function.forEach);

alert(Object.forEach === Function.forEach); // true