js中Object.__proto__===Function.prototype

参考：http://stackoverflow.com/questions/650764/how-does-proto-differ-from-constructor-prototype

http://blog.rainy.im/

__proto__ is the actual object that is used in the lookup chain to resolve methods, etc. prototype is the object that is used to build __proto__ when you create an object with new:

( new Foo ).__proto__ === Foo.prototype
( new Foo ).prototype === undefined

The most surprising thing for me was discovering that Object.__proto__ points to Function.prototype, instead of Object.prototype, but I'm sure there's a good reason for that :-)

I think the class Object itself is an instance of Function, that's why Object.__proto__ === Function.prototype.

The reason why Object.__proto__ points to Function.prototype is because Object() by itself is a native function that instantiates an empty object. Therefore, Object() is a function. You'll find that all the other major native types' __proto__ properties point to Function.prototype. Object, Function, String, Number, and Array all inherit the Function prototype.

This means that adding to Function.prototype will automatically reflect on all objects whose __proto__ is referencing the Function.prototype.

For example, look the map below:

Furthermore, even the class Function itself is an instance of Function itself, that is Function.__proto__ === Function.prototype, that's also why Function === Function.constructor

Further furthermore, the regular class Cat is an instance of Function, that is Cat.__proto__ === Function.prototype.

The reason for the above is, when we create a class in JavaScript, actually, we are just creating a function, which should be an instance of Function. Object and Function are just special, but they are still classes, while Cat is a regular class.

As a matter of factor, in Google Chrome JavaScript engine, the following 4:

• Function.prototype
• Function.__proto__
• Object.__proto__
• Cat.__proto__

They are all === (absolutely equal) to the other 3, and their value is function Empty() {}

> Function.prototype
  function Empty() {}
> Function.__proto__
  function Empty() {}
> Object.__proto__
  function Empty() {}
> Cat.__proto__
  function Empty() {}
> Function.prototype === Function.__proto__
  true
> Function.__proto__ === Object.__proto__
  true
> Object.__proto__ === Cat.__proto__
  true

prototype-chain