emmiter.js

function create () {
  const events = {}

  function off (n, callback) {
    if (!events[n]) {
      return
    }

    events[n] = events[n].filter(fn => fn !== callback)
  }

  function on (name, callback) {
    if (!events[name]) {
      events[name] = []
    }

    if (!callback) {
      throw new Error('No callback bro')
    }

    if (!events[name].includes(callback)) {
      events[name].push(callback)
    }

    return off.bind(null, name, callback)
  }

  function emit (n, args) {
    if (!events[n]) {
      return
    }

    events[n].forEach(fn => fn({ ...args, type: n }))
  }

  function once (name, callback) {
    on(name, (args) => {
      callback(args)
      off(name, callback.bind(null, args))
    })

    return off.bind(null, name, callback)
  }

  return { on, emit, off, events, once }
}

module.exports = { create }