js实现继承的5种方式

1.对象冒充：

function Parent(username){
    this.username = username;
    this.hello = function(){
         alert(this.username);
    }
}

function Child(username,password){
    this.method = Parent;
    this.method(username);//最关键的一行
    delete this.method;
    this.password = password;
    this.world = function(){
         alert(this.password);
    }
}

var parent = new Parent("zhangsan");
var child = new Child("lisi","123456");
parent.hello();
child.hello();
child.world();

2.call()方法：

function Parent(username){
    this.username = username;
    this.hello = function(){
         alert(this.username);
    }
}

 function Child(username,password){
     Parent.call(this,username);
     this.password = password;
     this.world = function(){
          alert(this.password);
     }
 }

var parent = new Parent("zhangsan");
var child = new Child("lisi","123456");
parent.hello();
child.hello();
child.world();

3.apply()方法：

function Parent(username){
    this.username = username;
    this.hello = function(){
         alert(this.username);
    }
}

function Child(username,password){
    Parent.apply(this,new Array(username));
    this.password = password;
    this.world = function(){
         alert(this.password);
    }
}

var parent = new Parent("zhangsan");
var child = new Child("lisi","123456");
parent.hello();
child.hello();
child.world();

4.原型链：

function Person(){}
Person.prototype.hello = "hello";
Person.prototype.sayHello = function(){
     alert(this.hello);
}

function Child(){}
Child.prototype = new Person();//这行的作用是：将Parent中将所有通过prototype追加的属性和方法都追加到Child，从而实现了继承
Child.prototype.world = "world";
Child.prototype.sayWorld = function(){
     alert(this.world);
}

var c = new Child();
c.sayHello();
c.sayWorld();

5.call()方法与原型链混合：

function Parent(hello){
    this.hello = hello;
}
Parent.prototype.sayHello = function(){
     alert(this.hello);
}

function Child(hello,world){
    Parent.call(this,hello);//将父类的属性继承过来
    this.world = world;//新增一些属性
}
Child.prototype = new Parent();//将父类的方法继承过来
Child.prototype.sayWorld = function(){//新增一些方法
     alert(this.world);
}

var c = new Child("zhangsan","lisi");
c.sayHello();
c.sayWorld();