fullscreen function

fs.js

var $ = document.querySelector.bind(document);

// Once the user clicks a custom fullscreen button
$(playButtonClass).addEventListener('click', function(){
  // Play video and go fullscreen
  player.playVideo();

  var playerElement = $(playerWrapperClass);
  var requestFullScreen = playerElement.requestFullScreen || playerElement.mozRequestFullScreen || playerElement.webkitRequestFullScreen;
  if (requestFullScreen) {
    requestFullScreen.bind(playerElement)();
  }
})