jQuery-源码阅读，JavaScript原生继承方式与jQuery中的继承

来源：互联网发布：安装联系人软件编辑：程序博客网时间：2024/06/01 21:00

JavaScript中继承方法有以下几种：

1.原型链继承：

function Book (name,author){    this.name=name;    this.author=author;}Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};function JavaScript(){}JavaScript.prototype=new Book("JavaScript","Nicholas");var js1=new JavaScript();var js2=new JavaScript();js1.tell();//Book:JavaScript Author:Nicholasjs2.tell();//Book:JavaScript Author:Nicholas

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：

function Book (name,author){this.name=name;this.author=[author];}Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};function JavaScript(){}JavaScript.prototype=new Book("JavaScript","Nicholas");var js1=new JavaScript();var js2=new JavaScript();js1.author.push("C.Zakas");js2.tell();//Book:JavaScript Author:Nicholas,C.Zakas

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：

        function Book (name,author){this.name=name;this.author=author;}Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};function JavaScript(){}JavaScript.prototype=new Book("JavaScript","Nicholas");var js1=new JavaScript();var js2=new JavaScript();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"));//trueconsole.log(js2.hasOwnProperty("author"));//falsejs1.tell();//Book:JavaScript Author:C.Zakas js2.tell();//Book:JavaScript Author:Nicholas

2.构造函数继承：

       function Book (name,author){this.name=name;this.author=author;}Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};function JavaScript(){Book.apply(this,arguments);}var js1=new JavaScript("JavaScript","Nicholas");var js2=new JavaScript("JavaScriopt","C.Zakas");console.log("js1:"+js1.author+" js2:"+js2.author);//js1:Nicholas js2:C.Zakasjs1.tell();//Uncaught TypeError: js1.tell is not a functionjs2.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：

        function Book (name,author){this.name=name;this.author=author;}Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};function JavaScript(){Book.apply(this,arguments);}JavaScript.prototype=new Book();var js1=new JavaScript("JavaScript","Nicholas");var js2=new JavaScript("JavaScriopt","C.Zakas");console.log("js1:"+js1.author+" js2:"+js2.author);//js1:Nicholas js2:C.Zakasjs1.tell();//Book:JavaScript Author:Nicholasjs2.tell();//Book:JavaScriopt Author:C.Zakas        console.log(js1.tell===js2.tell);//true

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：

        function Book (name,author){this.name=name;this.author=author;}Book.prototype.tell=function(){console.log("Book:"+this.name+" Author:"+this.author);};function JavaScript(){Book.apply(this,arguments);}JavaScript.prototype=Object.create(Book.prototype);JavaScript.prototype.constructor=JavaScript;var js1=new JavaScript("JavaScript","Nicholas");var js2=new JavaScript("JavaScriopt","C.Zakas");console.log("js1:"+js1.author+" js2:"+js2.author);//js1:Nicholas js2:C.Zakasjs1.tell();//Book:JavaScript Author:Nicholasjs2.tell();//Book:JavaScriopt Author:C.Zakasconsole.log(js1.tell===js2.tell);//true

由以上分析可以看出，JavaScript中原生的继承方式各有利弊，在jQuery中选择了另一种继承方式，拷贝继承。jQuery的拷贝继承分为两种：深拷贝和浅拷贝。默认为浅拷贝。其实现请见：http://blog.csdn.net/qiqingjin/article/details/50761517。

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