List all event listeners in a document

allEventListeners.js

function allEventListeners(){
  const eventNames = Object.keys(window).filter(key => /^on/.test(key))
  return [...document.querySelectorAll('*'), document].flatMap((node) => eventNames
    .filter(event => node[event])
    .map(event => {
       return {
         node,
         event,
         listener: (typeof node[event] === 'function') ? node[event].toString() : node[event]
       }
    })
  )
}

console.table(allEventListeners())