Detect fullscreen on iframe

gistfile1.txt

function changeHandler(e) {
   console.log('fullscreen');
   document.webkitCancelFullScreen()
   //document.documentElement.webkitRequestFullScreen();
}

document.addEventListener("fullscreenchange", changeHandler, false);
document.addEventListener("webkitfullscreenchange", changeHandler, false);
document.addEventListener("mozfullscreenchange", changeHandler, false);