上篇文章中我們講了些類的基本概念，其中提到ES6中的類語法是對原型繼承的一種封裝。JS的原型繼承一共有兩條原型鏈，顯示和隱式，那麼在類繼承的語法中，這兩條原型鏈又是怎麼樣的呢？

繼續使用上篇文章中的例子：

class Point{...}

class ColorPoint extends Point{...}

var p = new Point(...),cp = new ColorPoint(...);

typeof Point// function
console.log(Object.getOwnPropertyNames(Point))//["length", "name", "prototype", "getDesc", "TAG"]

typeof ColorPoint //function
console.log(Object.getOwnPropertyNames(ColorPoint))//["length","name","prototype"]
 

console.log(typeof Point.prototype);//object
console.log(Object.getOwnPropertyNames(Point.prototype));//["constructor","toString"]
Point.prototype.constructor === Point//true

console.log(typeof ColorPoint.prototype);//object
console.log(Object.getOwnPropertyNames(ColorPoint.prototype));//["contructor","toString"]
ColorPoint.prototype.constructor === ColorPoint
 

Object.getPrototypeOf(Object.prototype) === null

Object.getPrototypeOf(Function.prototype) === Object.prototype

Object.getPrototypeOf(Point) === Function.prototype//true

Object.getPrototypeOf(ColorPoint) === Point//true

弄清了類之間的繼承關係，在來看例項之間的繼承關係：

Object.getPrototypeOf(cp) === ColorPoint.prototype//true

Object.getPrototypeOf(ColorPoint.prototype) === Point.prototype//true

Object.getPrototypeOf(Point.prototype) === Object.prototype//true

Object.getPrototypeOf(Object.prototype) === null//true

Object.getPrototypeOf(p) === Point.prototype//true

看了這個圖是不是腦子裡有了更形象的印象了，要熟記這個原型鏈，對以後複雜的應用會有很大幫助。

我們看幾個其它的例子：

class C{}

Object.getPrototypeOf(C) === Function.prototype//true
Object.getPrototypeOf(C.prototype) === Object.prototype//true

class C extends Object {
}

Object.getPrototypeOf(C) === Object//true
Object.getPrototypeOf(C.prototype) === Object.prototype//true

class C extends null {
}

Object.getPrototypeOf(C) === Function.prototype //true
Object.getPrototypeOf(C.prototype) === null//true

*以上全部程式碼在Chrome 47下通過測試