Javascript原型链和原型的一个误区

作者: Laruence 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:

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