title: Reliably determining full screen size in ES6
body: <p>I have a  in my document which I scale to full screen using the full screen JS API div.fullscreenRequest(). I find out how large the full screen actually is only after it has been activated, i.e., the fullscreenchange event has fired. In this event, I make some computations (original size of div versus new scaled-up size) so I can apply some transformations to the div to make it look right.</p>
  <p>The issue I am having is that determining the full screen size is highly unreliable. In the fullscreenchange event, if I do detect that the full screen mode has been activated, and I use screen.width and screen.height, respectively, I sometimes get the correct values back (1920 x 1080) but sometimes I get 1920 x 948 for no apparent reason, non-deterministically. It appears that the event fires in some sort of racy way while the screen is still switching to full screen mode?</p>
  <p>What is the reliable way of determining the full screen resolution?</p>