Command对象（SimpleCommand或者MacroCommand)是无状态的；只有在需要的时候（Controller收到相应的Notification）才会被创建，并且被执行（调用execute方法),每次调用sendNotification才创建对象并调用execute
proxy，Mediator在注册时才创建
https://www.cnblogs.com/studynote/archive/2013/06/12/3132194.html https://github.com/PureMVC/puremvc-typescript-multicore-framework/blob/master/src/org/puremvc/typescript/multicore/patterns/facade/Facade.ts https://www.jianshu.com/p/b0f9d2b3e547
