function Parent(username){
  this.username = username;
  this.hello = function(){
   alert(this.username);
  }
}
function Child(username,password){
  //通過以下3行實(shí)現(xiàn)將Parent的屬性和方法追加到Child中，從而實(shí)現(xiàn)繼承
  //第一步：this.method是作為一個(gè)臨時(shí)的屬性，并且指向Parent所指向的對(duì)象，
  //第二步：執(zhí)行this.method方法，即執(zhí)行Parent所指向的對(duì)象函數(shù)
  //第三步：銷毀this.method屬性，即此時(shí)Child就已經(jīng)擁有了Parent的所有屬性和方法 
  this.method = Parent;
  this.method(username);//最關(guān)鍵的一行
  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();

function test(str){
  alert(this.name + " " + str);
}
var object = new Object();
object.name = "zhangsan";
test.call(object,"langsin");//此時(shí)，第一個(gè)參數(shù)值object傳遞給了test類(即方法)中出現(xiàn)的this，而第二個(gè)參數(shù)"langsin"則賦值給了test類(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(); 

function Person(){ 
} 
Person.prototype.hello = "hello"; 
Person.prototype.sayHello = function(){ 
  alert(this.hello); 
} 
function Child(){ 
} 
Child.prototype = new Person();//這行的作用是：將Parent中將所有通過prototype追加的屬性和方法都追加到Child，從而實(shí)現(xiàn)了繼承 
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);//將父類的屬性繼承過來 
  this.world = world;//新增一些屬性 
} 
Child.prototype = new Parent();//將父類的方法繼承過來 
Child.prototype.sayWorld = function(){//新增一些方法 
  alert(this.world); 
} 
var c = new Child("zhangsan","lisi"); 
c.sayHello(); 
c.sayWorld();