Detecting device orientation change in javascript

I’ve recently been getting stuck back into mobile app development in javascript. Being able to detect orientation change allows is really useful, It can be used to force users into a specific orientation by throwing up a notification panel saying “Please hold the device in landscape for this app”. Such scenarios are particularly important when developing games for mobile browsers.

<script>           
  function doOnOrientationChange()
  {
    switch(window.orientation) 
    {  
      case -90:
      case 90:
        alert('landscape');
        break; 
      default:
        alert('portrait');
        break; 
    }
  }

  window.addEventListener('orientationchange', doOnOrientationChange);

  // Initial execution if needed
  doOnOrientationChange();
</script>