Java程序员从笨鸟到菜鸟之（二十九）javascript对象的创建和继承实现

 

javascript对象的创建

 

JavaScript中定义对象的几种方式（JavaScript中没有类的概念，只有对象）： 

1） 基于已有对象扩充其属性和方法： 

var object = new Object();

object.name = "zhangsan";
object.sayName = function(name)
{
    this.name = name;
    alert(this.name);
}

object.sayName("lisi");

 

 

2）工厂方式 

//工厂方式创建对象

/*
function createObject()
{
    var object = new Object();

    object.username = "zhangsan";
    object.password = "123";

    object.get = function()
    {
        alert(this.username + ", " + this.password);
    }

    return object;
}

var object1 = createObject();
var object2 = createObject();

object1.get();

 

 

带参数的构造方法： 

function createObject(username, password)
{
    var object = new Object();

    object.username = username;
    object.password = password;

    object.get = function()
    {
        alert(this.username + ", " + this.password);
    }

    return object;
}

var object1 = createObject("zhangsan", "123");
object1.get();

 

让一个函数对象被多个对象所共享，而不是每一个对象拥有一个函数对象。 

function get()
{
    alert(this.username + ", " + this.password);
}

function createObject(username, password)
{
    var object = new Object();

    object.username = username;
    object.password = password;

    object.get = get;

    return object;
}

var object = createObject("zhangsan", "123");
var object2 = createObject("lisi", "456");

object.get();
object2.get();

 

 

 

3）构造函数方式 

function Person()
{
    //在执行第一行代码前，js引擎会为我们生成一个对象
 this.username = "zhangsan";
 this.password = "123";

 this.getInfo = function()
 {
  alert(this.username + ", " + this.password);
 }

 //此处有一个隐藏的return语句，用于将之前生成的对象返回
}

var person = new Person();
person.getInfo();

 

         可以在构造对象时传递参数 

function Person(username, password)
{
    this.username = username;
    this.password = password;

    this.getInfo = function()
    {
        alert(this.username + ", " + this.password);
    }
}

var person = new Person("zhangsan", "123");
person.getInfo();

 

 

4）原型（“prototype”）方式 

//使用原型（prototype）方式创建对象

/*
function Person()
{

}

Person.prototype.username = "zhangsan";
Person.prototype.password = "123";

Person.prototype.getInfo = function()
{
    alert(this.username + ", " + this.password);
}

var person = new Person();
var person2 = new Person();

person.username = "lisi";

person.getInfo();
person2.getInfo();
*/

 

function Person()
{

}

Person.prototype.username = new Array();
Person.prototype.password = "123";

Person.prototype.getInfo = function()
{
    alert(this.username + ", " + this.password);
}

var person = new Person();
var person2 = new Person();

person.username.push("zhangsan");
person.username.push("lisi");
person.password = "456";

person.getInfo();
person2.getInfo();

 

 

如果使用原型方式对象，那么生成的所有对象会共享原型中的属性，这样一个对象改变了该属性也会反应到其他对象当中。

单纯使用原型方式定义对象无法在构造函数中为属性赋初值，只能在对象生成后再去改变属性值。 

 使用原型+构造函数方式来定义对象，对象之间的属性互不干扰，各  个对象间共享同一个方法 

//使用原型+构造函数方式来定义对象

function Person()
{
    this.username = new Array();
    this.password = "123";
}

Person.prototype.getInfo = function()
{
    alert(this.username + ", " + this.password);
}

var p = new Person();
var p2 = new Person();

p.username.push("zhangsan");
p2.username.push("lisi");

p.getInfo();
p2.getInfo();

 

5）动态原型方式：在构造函数中通过标志量让所有对象共享一个方法，而每个对象拥有自己的属性。 

function Person()
{
    this.username = "zhangsan";
    this.password = "123";

    if(typeof Person.flag == "undefined")
    {
        alert("invoked");

        Person.prototype.getInfo = function()
        {
            alert(this.username + ", " + this.password);
        }

        Person.flag = true;
    }
}

var p = new Person();
var p2 = new Person();

p.getInfo();
p2.getInfo();

 

JavaScript中的继承。 

1） 对象冒充 

//继承第一种方式：对象冒充

function Parent(username)
{
    this.username = username;

    this.sayHello = function()
    {
        alert(this.username);
    }
}

function Child(username, password)
{
    //下面三行代码是最关键的代码
    this.method = Parent;
    this.method(username);
    delete this.method;

    this.password = password;

    this.sayWorld = function()
    {
        alert(this.password);
    }
}

var parent = new Parent("zhangsan");
var child = new Child("lisi", "1234");

parent.sayHello();

child.sayHello();
child.sayWorld();

 

 

 

2） call方法方式。 

call方法是Function对象中的方法，因此我们定义的每个函数都拥有该方法。可以通过函数名来调用call方法，call方法的第一个参数会被传递给函数中的this，从第2个参数开始，逐一赋值给函数中的参数。 

 

<p>//使用call方式实现对象的继承</p><p>function Parent(username)
{
 this.username = username;</p><p> this.sayHello = function()
 {
  alert(this.username);
 }
}</p><p>function Child(username, password)
{
 Parent.call(this, username);</p><p> this.password = password;</p><p> this.sayWorld = function()
 {
  alert(this.password);
 }
}</p><p>var parent = new Parent("zhangsan");</p><p>var child = new Child("lisi", "123");</p><p>parent.sayHello();</p><p>child.sayHello();
child.sayWorld();</p><p>
 </p><span style="font-size:18px;"><span style="color:#000000;"> </span></span>

 

 

3） apply方法方式 

//使用apply方法实现对象继承

function Parent(username)
{
    this.username = username;

    this.sayHello = function()
    {
        alert(this.username);
    }
}

function Child(username, password)
{
    Parent.apply(this, new Array(username));

    this.password = password;

    this.sayWorld = function()
    {
        alert(this.password);
    }
}


var parent = new Parent("zhangsan");
var child = new Child("lisi", "123");

parent.sayHello();

child.sayHello();
child.sayWorld();

 

 

4）原型链方式（无法给构造函数传参数） 

//使用原型链（prototype chain）方式实现对象继承

function Parent()
{

}

Parent.prototype.hello = "hello";
Parent.prototype.sayHello = function()
{
    alert(this.hello);
}

function Child()
{

}

Child.prototype = new Parent();

Child.prototype.world = "world";
Child.prototype.sayWorld = function()
{
    alert(this.world);
}

var child = new Child();

child.sayHello();
child.sayWorld();

 

 

5）混合方式（推荐） 

 

 

更多信息请查看 java进阶网 http://www.javady.com

//使用混合方式实现对象继承(推荐)

function Parent(hello)
{
    this.hello = hello;
}

Parent.prototype.sayHello = function()
{
    alert(this.hello);
}

function Child(hello, world)
{
    Parent.call(this, hello);

    this.world = world;
}

Child.prototype = new Parent();

Child.prototype.sayWorld = function()
{
    alert(this.world);
}

var child = new Child("hello", "world");

child.sayHello();
child.sayWorld();