JavaScript类的几种写法

我们常用的有以下几种方法来用JavaScript写一个“类”：

1. 构造函数(public属性和方法）

1: function Person(iName, iAge){

2:  this.name=iName; //public

3:  this.age=iAge; //public

4:  this.ShowStudent=function(){ //public

5:  alert(this.name);

6:  };

7: }

以上的属性和方法都是public的。下面的例子给出private和public的属性和方法。

2. 构造函数（public, private属性和方法）

1: function Person(iName, iAge){

2:  //private field

3:  　var name = iName;　　　　

4:  var age = iAge;

5:  　　　　

6:  //private method

7:  　var privatefn = function(){　　　　

8:  　　alert(name);

9:  　}

10:

11:  return {

12:  　　 //public field

13:  Name: "hello " + name,

14:  Age: "hello " + age,

15:

16:  ShowStudent: function(){

17:  privatefn();　

18:  alert(this.Name);　

19:  }

20:  };

21: }

调用：(new Person("xiao","10")).ShowStudent();

3. 原型方法（prototype）

1: function c(){}

2: c.prototype={

3:  name: "init value a",

4:  setName: function(iName){

5:  this.name=iName;

6:  },

7:  getName: function(){

8:  alert('hello from c, name: ' + this.name);

9:  }

10: };

11: (new c).getName(); // 输出hello from c, name: init value a

4. 构造函数+原型方法（prototype）

1: function Person(iName) {

2:  this.name = iName;

3: };

4:

5: Person.prototype={

6:  getName: function(){

7:  return this.name;

8:  }

9: };

10:

11: //调用

12: var b = new Person("jack");

13: alert(b.getName());

5. 构造函数+原型方法（prototype）- 节省内存的写法

1: function Person(iName, iAge){

2:  this.name=iName;

3:  this.age=iAge;

4:

5:  //对象实例都共享同一份方法不造成内存浪费

6:  if(typeof Person._initialized == "undefined"){

7:  Person.prototype.ShowStudent=function(){

8:  alert(this.name);

9:  };

10:Person._initialized=true;

11:  }

12: }

13: //调用

14: (new Person("jack","20")).ShowStudent();

以上的实现方法如果不用_initialized的方法，也可以指向一个外部函数，道理一样。

6. JavaScript类的单例（Singleton）模式写法

1: var MyNamespace = {};

2: MyNamespace.Singleton = (function() {

3:  var uniqueInstance; // Private attribute that holds the single instance.

4:function constructor() { // All of the normal singleton code goes here.

5:  // Private members.

6:  var privateAttribute1 = false;

7:  var privateAttribute2 = [1, 2, 3];

8:  function privateMethod1() {

9:  //...

10:}

11:  function privateMethod2(args) {

12:  //...

13:  }

14:  return { // Public members.

15:publicAttribute1: true,

16:  publicAttribute2: 10,

17:  publicMethod1: function() {

18:  // ...

19:  },

20:  publicMethod2: function(args) {

21:  // ...

22:  }

23:  }

24:  }

25:  return {

26:  getInstance: function() {

27:  if(!uniqueInstance) { // Instantiate only if the instance doesn't exist.

28:  uniqueInstance = constructor();

29:  }

30:  return uniqueInstance;

31:  }

32:  }

33: })();

34:

35: //调用:

36: MyNamespace.Singleton.getInstance().publicMethod1();