js的单例实现

• 方法一

//方案一 
    var SingletonTester = (function () { 
        //单例方法 
        function Singleton(args) { 
            var args = args || {}; 
            this.name = 'SingletonTester'; //方法对外的属性，另一种方式就是返回对象 
            this.pointX = args.pointX || 6; 
            this.pointY = args.pointY || 10; 
        } 

        //单例实例 
        var instance; 

        //返回对象 
        return { 
            name: 'SingletonTester', 

            getInstance: function (args) { 
                if (instance === undefined) { 
                    instance = new Singleton(args); 
                } 
                return instance; 
            } 
        }; 
    })(); //直接执行该方法 

    //测试 
    var test = SingletonTester.getInstance({ pointX: 5 }); 
    console.log(test.pointX);

• 方法二

function Universe() { 
      // 判断是否存在实例 
      if (typeof Universe.instance === 'object') { 
          return Universe.instance; 
      } 

      // 其它内容 
      this.start_time = 0; 
      this.bang = "Big"; 

      // 缓存 
      Universe.instance = this; 

      // 隐式返回this 
  } 

  // 测试 
  var uni = new Universe(); 
  var uni2 = new Universe(); 
  console.log(uni === uni2); // true