Javascript实现继承的5种方式

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);  
    }  
}  
function Child(firstname)  
{  
    this.parent=Parent;  
    this.parent(firstname);  
    delete this.parent;  
    this.saySomeThing=function()  
    {  
        console.log(this.fname);  
        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);  
    }  
}  
function Child(firstname)  
{  
  
    this.saySomeThing=function()  
    {  
        console.log(this.fname);  
        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);  
    }  
}  
function Child(firstname)  
{  
  
    this.saySomeThing=function()  
    {  
        console.log(this.fname);  
        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

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();