js是门灵活的语言，实现一种功能往往有多种做法,ECMAScript没有明确的继承机制，而是通过模仿实现的，根据js语言的本身的特性,js实现继承有以下通用的几种方式 1.使用对象冒充实现继承(该种实现方式可以实现多继承) 实现原理:让父类的构造函数成为子类的方法,然后调用该子类的方法,通过this关键字给所有的属性和方法赋值 ``` function Parent(firstname) { this.fname=firstname; this.age=40; this.sayAge=function() { console.log(this.age); //40 } } function Child(firstname) { this.parent=Parent; this.parent(firstname); delete this.parent; this.saySomeThing=function() { console.log(this.fname); //李 this.sayAge(); } } var mychild=new Child("李"); mychild.saySomeThing(); ``` 2.采用call方法改变函数上下文实现继承(该种方式不能继承原型链,若想继承原型链，则采用5混合模式) 实现原理:改变函数内部的函数上下文this,使它指向传入函数的具体对象 ``` function Parent(firstname) { this.fname=firstname; this.age=40; this.sayAge=function() { console.log(this.age); //40 } } function Child(firstname) { this.saySomeThing=function() { console.log(this.fname); //张 this.sayAge(); } this.getName=function() { return firstname; } } var child=new Child("张"); Parent.call(child,child.getName()); child.saySomeThing(); ``` 3.采用Apply方法改变函数上下文实现继承(该种方式不能继承原型链,若想继承原型链，则采用5混合模式) 实现原理:改变函数内部的函数上下文this,使它指向传入函数的具体对象 ``` function Parent(firstname) { this.fname=firstname; this.age=40; this.sayAge=function() { console.log(this.age); //40 } } function Child(firstname) { this.saySomeThing=function() { console.log(this.fname); //张 this.sayAge(); } this.getName=function() { return firstname; } } var child=new Child("张"); Parent.apply(child,[child.getName()]); child.saySomeThing(); ``` 4.采用原型链的方式实现继承 实现原理:使子类原型对象指向父类的实例以实现继承,即重写类的原型,弊端是不能直接实现多继承 ``` function Parent() { this.sayAge=function() { console.log(this.age); } } function Child(firstname) { this.fname=firstname; this.age=40; this.saySomeThing=function() { console.log(this.fname); this.sayAge(); } } Child.prototype=new Parent(); var child=new Child("张"); child.saySomeThing(); ``` 5.采用混合模式实现继承 ``` function Parent() { this.sayAge=function() { console.log(this.age); } } Parent.prototype.sayParent=function() { alert("this is parentmethod!!!"); } function Child(firstname) { Parent.call(this); this.fname=firstname; this.age=40; this.saySomeThing=function() { console.log(this.fname); this.sayAge(); } } Child.prototype=new Parent(); var child=new Child("张"); child.saySomeThing(); child.sayParent(); ```