https://bigfrontend.dev/zh/problem/create-an-Event-Emitter
    [zhika]

    1. class EventEmitter {
    3.   constructor() {
    4.     this.subs = {};
    5.   }
    7.   subscribe(eventName, callback) {
    8.     this.subs[eventName] ??= new Map();
    10.     const key = Symbol();
    11.     this.subs[eventName].set(key, callback);
    13.     return {
    14.       release: () => {
    15.         this.subs[eventName].delete(key);
    16.       }
    17.     }
    18.   }
    20.   emit(eventName, ...args) {
    21.     console.log(this.subs[eventName]);
    22.     for(const callback of this.subs[eventName].values()) {
    23.       try {
    24.         callback.apply(this,...args);
    25.       } catch (e) {
    26.         // Make sure to catch any errors - I was asked this in interview
    27.       }
    28.     }
    29.   }
    30. }
    32. const emitter = new EventEmitter()
    33. function callback1(...args){console.log(this,'111',args)}
    34. function callback2(...args){console.log(this,'222',args)}
    35. const sub1  = emitter.subscribe('event1', callback1)
    36. const sub2 = emitter.subscribe('event2', callback2)
    37. const sub3 = emitter.subscribe('event1', callback2)
    38. sub1.release()
    39. // sub3.release()
    40. console.log(emitter.emit('event1', 1, 2));