其实就是发布订阅模式

    1. export class BusEvent {
    2.     constructor() {
    3.         this.handlers = new Map();
    4.     }
    6.     on(type, handler) {
    7.         const handlers = this.handlers.get(type);
    8.         const added = handlers && handlers.push(handler);
    9.         if (!added) {
    10.             this.handlers.set(type, [handler]);
    11.         }
    12.     }
    14.     off(type, handler) {
    15.         const handlers = this.handlers.get(type);
    16.         if (handlers) {
    17.             handlers.splice(handlers.indexOf(handler) >>> 0, 1)
    18.         }
    19.     }
    21.     emit(type, evt) {
    22.         (this.handlers.get(type) || []).slice().map(handler => handler(evt));
    23.     }
    24. }