js实现单例

单例无外乎每次调用返回的都是同一个对象，可以利用闭包实现

　　　　　　　function Singleton(){

                this.data = "singleton";

            }

            Singleton.getInstance = (function(){

                var instance;

                return function(){

                    instance = instance ? instance:new Singleton;

                    return instance;

                }

            })();

            var sa = Singleton.getInstance();

            var sb = Singleton.getInstance();

            console.log(sa === sb);

            console.log(sa.data);

输出结果

这种方式比较简单，Singleton类暴露全局，直接使用Singleton.getInstance()即可。

还有种情况，假设不想暴露Singleton，可以

　　　　　　　var SingletonA = (function(){

                var instance = null;

                function Singleton(){

                    this.init();

                }

                Singleton.prototype.init = function(){

                    this.data = "SingletonA";

                }

                return function(){

                    if(instance == null){

                        instance = new Singleton();

                    }

                    return instance;

                };

            })();

            var b = SingletonA();

            var c = SingletonA();

            console.log(b === c);

            console.log(b.data);

输出

还有一种

　　　　　　　var SingletonF = function(){

                if(SingletonF.instance){

                    console.log("不能new");

                }

                this.name = "gggg";

            };

            SingletonF.getInstance = function(name){

                if(SingletonF.instance == null){

                    SingletonF.instance = new SingletonF();

                }

                return SingletonF.instance;

            }

            var s1 = SingletonF.getInstance("ccc");

            var s2 = SingletonF.getInstance("def");

            console.log(s1 === s2);

            console.log(s1.name);

写法基本上大同小异，只要保证instance唯一就行了