1.function的静态变量

2.重写function的构造函数（其实就是把function覆盖)

3.封装

var Universe;        (function () {            var instance;            Universe = function () {                if (instance) {                    return instance;                }                instance = this;                this.name = "hongda";                this.age = 28;            };        } ());        var uni = new Universe();        var uni2 = new Universe();        console.log(uni === uni2);