Event

2023-06-16 10:32:28

实现一个事件收发器 Event 类，继承自此类的对象拥有 on, off, once 和 trigger 方法

// 满足下例使用示例：
const event = new Event();
function log(val) {console.log(val);};
event.on('foo_event', log);
event.trigger('foo_event', 'abc'); // 打印出 abc
event.off('foo_event', log);
event.trigger('foo_event', 'abc'); // 打印出 undefined

class Event {
  constructor() {
    this.events = {};
  }

  // 注册事件
  on(eventName, callback) {
    if (!this.events[eventName]) {
      this.events[eventName] = [];
    }
    this.events[eventName].push(callback);
  }

  // 关闭事件
  off(eventName, callback) {
    if (this.events[eventName]) {
      if (callback) {
        this.events[eventName] = this.events[eventName].filter(cb => cb !== callback);
      } else {
        delete this.events[eventName];
      }
    }
  }

  // 只执行一次事件
  once(eventName, callback) {
    const onceCallback = (...args) => {
      callback(...args);
      this.off(eventName, onceCallback);
    };
    this.on(eventName, onceCallback);
  }

  // 触发事件
  trigger(eventName, ...args) {
    const eventCallbacks = this.events[eventName];
    if (eventCallbacks) {
      eventCallbacks.forEach(callback => callback(...args));
    }
  }
}