events.js

class EventEmitter {
  constructor() {
    this.listeners = {}
  }
  
  addListener(event, fn) {
    if (!this.listeners[event]) {
      this.listeners[event] = []
    }
    this.listeners[event].push(fn)
  }
  
  removeListener(event, fn) {
    if (!this.listeners[event]) {
      this.listeners[event] = []
    }
    for (let i = 0; i < this.listeners[event].length; ++i) {
      if (this.listeners[event][i] === fn) {
        this.listeners[event].splice(i, 1)
        break
      }
    }
  }
  
  emit(event, payload) {
    if (!this.listeners[event]) {
      this.listeners[event] = []
    }
    for (const handler of this.listeners[event]) {
      handler(payload)
    }
  }
}

// usage
const events = new EventEmtiter()
events.addListener('fart', function (person) { console.log(person, 'farted') })
events.emit('fart', 'paul')