// 订阅发布模式class EventEmitter {  constructor() {    this._events = {};  }  on(name, callback) {    if (this._events[name]) {      this._events[name].push(callback);    } else {      this._events[name] = [callback];    }  }  emit(name) {    if (this._events[name]) {      this._events[name].forEach(cb => cb());    }  }  remove(name, callback) {    if (this._events[name]) {      this._events[name] = this._events[name].filter(cb => cb !== callback);    }  }  once(name, callback) {    const fn = () => {      callback();      this.remove(name, fn);    };    this.on(name, fn);  }}const event = new EventEmitter();const func1 = () => {  console.log('func1');};const func2 = () => {  console.log('func2');};const func3 = () => {  console.log('func3');};event.on('datas', func1);event.on('datas', func2);event.once('datas', func3);event.emit('datas');event.remove('datas', func1);event.emit('datas');