Attempt to spy on addEventListener

spy-add-event-listener.js

  window.__numDomListeners = 0

  function spyAddListener (proto) {
    const addEventListener = proto.addEventListener
    proto.addEventListener = function () {
      window.__numDomListeners++
      console.log('add', this, arguments)
      return addEventListener.apply(this, arguments)
    }
  }

  function spyRemoveListener (proto) {
    const removeEventListener = proto.removeEventListener
    proto.removeEventListener = function () {
      window.__numDomListeners--
      console.log('remove', this, arguments)
      return removeEventListener.apply(this, arguments)
    }
  }

  function spy (proto) {
    spyAddListener(proto)
    spyRemoveListener(proto)
  }

  spy(Element.prototype)
  spy(document)
  spy(window)