events_vanilla.js

window.functSubscribeElement = function () {
  var elem = document.getElementById('test')
  elem.addEventListener('event', (event) => console.log(event.detail), false)
  return elem
}

window.eventDispatch = function (elem) {
  var event = new CustomEvent('event', {
    detail: {
      value: 'hello'
    }
  })
  elem.dispatchEvent(event)
}

const element = functSubscribeElement()

eventDispatch(element)