JavaScript 五种(构造方式)继承

 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();

 1 function test(str){
 2     alert(this.name + " " + str);
 3   }
 4   var object = new Object();
 5   object.name = "zhangsan";
 6   test.call(object,"langsin");//此时，第一个参数值object传递给了test类(即方法)中出现的this，而第二个参数"langsin"则赋值给了test类(即方法)的str
 7 
 8   function Parent(username){
 9     this.username = username;
10     this.hello = function(){
11       alert(this.username);
12     }
13   }
14   function Child(username,password){
15     Parent.call(this,username);
16    
17     this.password = password;
18     this.world = function(){
19       alert(this.password);
20     }
21   }
22   var parent = new Parent("zhangsan");
23   var child = new Child("lisi","123456");
24   parent.hello();
25   child.hello();
26   child.world();

 1 function Parent(username){
 2     this.username = username;
 3     this.hello = function(){
 4       alert(this.username);
 5     }
 6   }
 7   function Child(username,password){
 8     Parent.apply(this,new Array(username));
 9    
10     this.password = password;
11     this.world = function(){
12       alert(this.password);
13     }
14   }
15   var parent = new Parent("zhangsan");
16   var child = new Child("lisi","123456");
17   parent.hello();
18   child.hello();
19   child.world();

 1  function Person(){
 2   }
 3   Person.prototype.hello = "hello";
 4   Person.prototype.sayHello = function(){
 5     alert(this.hello);
 6   }
 7  
 8   function Child(){
 9   }
10   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
11   Child.prototype.world = "world";
12   Child.prototype.sayWorld = function(){
13     alert(this.world);
14   }
15  
16   var c = new Child();
17   c.sayHello();
18   c.sayWorld();

 1 function Parent(hello){
 2     this.hello = hello;
 3   }
 4   Parent.prototype.sayHello = function(){
 5     alert(this.hello);
 6   }
 7 
 8   function Child(hello,world){
 9     Parent.call(this,hello);//将父类的属性继承过来
10     this.world = world;//新增一些属性
11   }
12 
13   Child.prototype = new Parent();//将父类的方法继承过来
14 
15   Child.prototype.sayWorld = function(){//新增一些方法
16     alert(this.world);
17   }
18 
19   var c = new Child("zhangsan","lisi");
20   c.sayHello();
21   c.sayWorld();