FE-Note ｜晨风笔记

const EventEmitter = require('events');
// const EventEmitter=require('./index');

const event = new EventEmitter();

const say = (name) => console.log('say', name);
const run = (name) => console.log('run', name);

/**
 * event.on('print',say);
 * event.on('print',run);
 * event.emit('print','cc')
 */

event.once('print', say);
event.once('print', run);

event.off('print', say);
event.emit('print', 'cc');
event.emit('print', 'wgs');

class EventEmitter {
  constructor() {
    this._events = {};
  }
  on(eventName, fn) {
    (this._events[eventName] || (this._events[eventName] = [])).push(fn);
  }
  emit(eventName, ...args) {
    const curEventArr = this._events[eventName];
    if (curEventArr) {
      curEventArr.forEach((event) => event(...args));
    }
  }
  off(eventName, fn) {
    this._events[eventName] = this._events[eventName].filter(
      (event) => event !== fn && event.l !== fn,
    );
  }
  once(eventName, fn) {
    const callback = (...args) => {
      fn(...args);
      this.off(eventName, fn);
    };
    callback.l = fn;
    this.on(eventName, callback);
  }
}