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

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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：

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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

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//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：

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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。

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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

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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

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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

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//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();

*/

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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

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//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。

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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

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//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。

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<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

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//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）

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//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）

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//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();