Simple and no-deps EventEmitter implement for Browser

EventBus.js

export default class EventBus {
  constructor () {
    this.bus = document.createElement('span')
  }

  on (eventName, fn) {
    const handler = event => {
      fn && fn(...event.params)
    }
    this.bus.addEventListener(eventName, handler)

    fn.__off__ = () => {
      this.bus.removeEventListener(eventName, handler)
    }
  }

  emit (eventName, ...args) {
    const event = new window.Event(eventName)
    event.params = args || []
    this.bus.dispatchEvent(event)
  }

  off (eventName, fn) {
    typeof fn.__off__ === 'function' && fn.__off__()
  }
}