[转]JS继承的5种实现方式

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(); 

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(); 

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();