Attach multiple onError or onLoad listeners

attach-multiple-onerror-listeners.js

// Fork of https://gist.github.com/alexreardon/8833460
function addWindowEvent(event, fn) {
  const existing = window[event]
  if (typeof existing !== 'function') return fn
  return function () {
    existing.apply(window, arguments)
    fn.apply(window, arguments)
  }
}

const onError = addWindowEvent.bind(null, 'onerror')
const onLoad = addWindowEvent.bind(null, 'onload')

window.onerror = onError((msg) => {
  console.log('msg', msg)
})
window.onerror = onError((msg) => {
  console.log('msg2', msg)
})
window.onerror = onError((msg) => {
  console.log('msg3', msg)
})

setTimeout(function() {
  throw new Error('test')
}, 3000)