javascript设计模式——Singleton

单例模式指的是只能被实例化一次。

推荐阅读：

http://blog.mgechev.com/2014/04/16/singleton-in-javascript/

比较通用的一种Singleton模式

var mySingleton = (function () {
  // Instance stores a reference to the Singleton
  var instance;
  function init() {
    // Singleton
    // Private methods and variables
    function privateMethod(){
        console.log( "I am private" );
    }
    var privateVariable = "Im also private";
    var privateRandomNumber = Math.random();
    return {
      // Public methods and variables
      publicMethod: function () {
        console.log( "The public can see me!" );
      },
      publicProperty: "I am also public",
      getRandomNumber: function() {
        return privateRandomNumber;
      }
    };
  };
  return {
    // Get the Singleton instance if one exists
    // or create one if it doesn‘t
    getInstance: function () {
      if ( !instance ) {
        instance = init();
      }
      return instance;
    }
  };
})();
var singleA = mySingleton.getInstance();
var singleB = mySingleton.getInstance();
console.log( singleA === singleB); // true

这种写法的好处有

1.只能实例化一次

2.可以存在私有函数

3.变量不可访问，不容易被修改。