Count all event listeners

count-event-listeners.js

Array.from(document.querySelectorAll('*'))
  .reduce(function(pre, dom){
    var evtObj = getEventListeners(dom)
    Object.keys(evtObj).forEach(function (evt) {
      if (typeof pre[evt] === 'undefined') {
        pre[evt] = 0
      }
      pre[evt] += evtObj[evt].length
    })
    return pre
  }, {})

And a fun way to filter down the DOM nodes for other analysis, discarding things like emotions style tags, boilerplate, etc.
Array.from(document.querySelectorAll('*')).filter((i) => ['SCRIPT', 'STYLE', 'META', 'HEAD', 'TITLE', 'BODY', 'HTML'].indexOf(i.tagName) < 0)