原生继承的三种方式

1.原型链继承：

functionBook (name,author){

this.name=name;

this.author=author;

}

Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};

functionJavaScript(){}

JavaScript.prototype=newBook("JavaScript","Nicholas");

varjs1=newJavaScript();

varjs2=newJavaScript();

js1.tell();

js2.tell();

可以发现，原型链继承有一个问题，那就是父类中的私有属性，会因为父类作为子类原型构建原型链，使得子类所有实例所共享。当我们通过一个实例修改共享属性时，其他实例也将受到影响：

functionBook (name,author){

this.name=name;

this.author=[author];

}

Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};

functionJavaScript(){}

JavaScript.prototype=newBook("JavaScript","Nicholas");

varjs1=newJavaScript();

varjs2=newJavaScript();

js1.author.push("C.Zakas");

js2.tell();

但是当你直接为实例中属性赋值时，是在实例中重新定义了一个对应属性，而不是在修改原型中属性：

functionBook (name,author){

this.name=name;

this.author=author;

}

Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};

functionJavaScript(){}

JavaScript.prototype=newBook("JavaScript","Nicholas");

varjs1=newJavaScript();

varjs2=newJavaScript();

js1.author="C.Zakas";

//并不是js1没有影响js2，而是在js1中创建了新author属性

console.log(js1.hasOwnProperty("author"));//true

console.log(js2.hasOwnProperty("author"));//false

js1.tell();//Book:JavaScript Author:C.Zakas

js2.tell()

2.构造函数继承：

functionBook (name,author){

this.name=name;

this.author=author;

}

Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};

functionJavaScript(){

Book.apply(this,arguments);

}

varjs1=newJavaScript("JavaScript","Nicholas");

varjs2=newJavaScript("JavaScriopt","C.Zakas");

console.log("js1:"+js1.author+" js2:"+js2.author);//js1:Nicholas js2:C.Zakas

js1.tell();//Uncaught TypeError: js1.tell is not a function

js2.tell();//Uncaught TypeError: js2.tell is not a function

构造函数继承，可以使每个子类实例有一份自己的属性，但是无法找到父类原型中的函数。

3.组合继承：

functionBook (name,author){

this.name=name;

this.author=author;

}

Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};

functionJavaScript(){

Book.apply(this,arguments);

}

JavaScript.prototype=newBook();

varjs1=newJavaScript("JavaScript","Nicholas");

varjs2=newJavaScript("JavaScriopt","C.Zakas");

console.log("js1:"+js1.author+" js2:"+js2.author);//js1:Nicholas js2:C.Zakas

js1.tell();//Book:JavaScript Author:Nicholas

js2.tell();

组合继承使得每个子类实例，既可以保存一份自己的属性，又可以共享同一个函数。

4.寄生组合继承：

functionBook (name,author){

this.name=name;

this.author=author;

}

Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};

functionJavaScript(){

Book.apply(this,arguments);

}

JavaScript.prototype=Object.create(Book.prototype);

JavaScript.prototype.constructor=JavaScript;

varjs1=newJavaScript("JavaScript","Nicholas");

varjs2=newJavaScript("JavaScriopt","C.Zakas");

console.log("js1:"+js1.author+" js2:"+js2.author);//js1:Nicholas js2:C.Zakas

js1.tell()；

js2.tell();

console.log(js1.tell===js2.tell);