js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: }

缺点很明显，类的属性和方法，很容易被外部修改。

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()); 

一般多会用上面这种写法。

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();