cross-device, modified to launch on click and only cancel on drag from top instead of toggling on click

fullscreen toggle

function toggleFullScreen() {
  var doc = window.document;
  var docEl = doc.documentElement;

  var requestFullScreen = docEl.requestFullscreen || docEl.mozRequestFullScreen || docEl.webkitRequestFullScreen || docEl.msRequestFullscreen;
  var cancelFullScreen = doc.exitFullscreen || doc.mozCancelFullScreen || doc.webkitExitFullscreen || doc.msExitFullscreen;

  // if(!doc.fullscreenElement && !doc.mozFullScreenElement && !doc.webkitFullscreenElement && !doc.msFullscreenElement) {
    requestFullScreen.call(docEl);
  // }
  // else {
  //   cancelFullScreen.call(doc);
  // }
}