闭包实现单体模式

//指定单体命名空间
const Ext = {};

//执行函数的结果返回给Ext.base
Ext.base=(function () {

    let singleton;



    //初始化函数
    function init() {

        //私有成员变量
        let a1 = "a1";
        let a2 = "a2";

        let f1 = function () {
            console.log("f1");
        };

        let f2 = function () {
            console.log("f2");
        } ;

        return {
            attr1: a1,
            attr2:a2,
            func1:f1,
            func2:f2,
        };
    }

    return {
        getInstance: function () {
            if(!singleton){ //单体未实例化则实例化接化单体
                singleton = init();
            }

            return singleton;
        }
    }

})();

let instance = Ext.base.getInstance();
console.log(instance.attr1);
instance.func1();
instance.func2();