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(); 

 call方法是Function类中的方法

  call方法的第一个参数的值赋值给类(即方法)中出现的this

  call方法的第二个参数开始依次赋值给类(即方法)所接受的参数 

  function test(str){

    alert(this.name + " " + str);

  }

  var object = new Object();

  object.name = "zhangsan";

  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 

  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(); 

 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、继承的第四种方式：原型链方式，即子类通过prototype将所有在父类中通过prototype追加的属性和方法都追加到Child，从而实现了继承

  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(); 

 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、继承的第四种方式：原型链方式，即子类通过prototype将所有在父类中通过prototype追加的属性和方法都追加到Child，从而实现了继承

  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(); 

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();