Event 封装

class Event {
  cache;
  constructor() {
    this.cache = {};
  }
  // 监听
  on(eventType, func) {
    // this.cache[eventType] = func
    (this.cache[eventType] || (this.cache[eventType] = [])).push(func);
  }
  // 移除监听
  off(eventType, func) {
    if (func) {
      let stack = this.cache[eventType];
      if (stack && stack.length > 0) {
        for (let j = 0; j < stack.length; j++) {
          if (stack[j] == func) {
            stack.splice(j, 1);
            break;
          }
        }
      }
    } else {
      delete this.cache[eventType];
    }
  }
  // 监听一次
  once(eventType, func) {
    function on() {
      this.off(eventType, on);
      func.apply(this, arguments);
    }
    this.on(eventType, on);
  }
  // 发布订阅通知
  emit(eventType, ...args) {
    const stack = this.cache[eventType];
    if (stack && stack.length > 0) {
      stack.forEach((item) => item.apply(this, args));
    }
  }
}

export default Event;