继承的几种方式

方法一：对象冒充

   

    function Parent(username){
        this.username = username;
        this.hello = function(){
            alert(this.username);
        } }
    function Child(username,password){
    //通过以下3行实现将Parent的属性和方法追加到Child中，从而实现继承
    // 第一步：this.method是作为一个临时的属性，并且指向Parent所指向的对象，
    // 第二步：执行this.method方法，即执行Parent所指向的对象函数
    // 第三步：销毁this.method属性，即此时Child就已经拥有了Parent的所有属性和方法
        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();

 方法二：call方式

 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();

方法三：apply方式

    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();