beforeunload must return a string and not prompt anything

[rudiedirkx]

It would be insanely annoying and obtrusive if the browser could hassle the client with custom confirm() popups onbeforeunload and choose if the user can close this window. (The user should have (and has) that power.)

The app now tries to prompt. Incorrect. Chrome dev tools tell me this: http://screencast.com/t/wzHmfxJG3c

Correct: https://developer.mozilla.org/en/DOM/window.onbeforeunload

window.onbeforeunload = function() {
  return 'You have unsaved changes. Are you sure?'
}

[LeaVerou]

THANK you! That will solve #30! Closing this though as it's a duplicate (github should really have a merge feature)