matchMedia Demo

mobileURLs.js

// matchMedia is supported and the device has a small screen
if ( "matchMedia" in window 
  && window.matchMedia( "(max-device-width: 800px)" ) 
) {
Array.prototype.forEach.call(
  // for each element matching the selector... 
  document.querySelectorAll( 
    "a[href*='youtube.com/watch'], a[href*='flickr.com']" 
  ),
  // ...replace the href with their mobile equivalent
  function( elem ) {
    if ( /flickr\.com\/?(.*)$/.test( elem.href ) ) {
      elem.href = "http://m.flickr.com/" + RegExp.$1;

    } else {
      elem.href = 
        "http://m.youtube.com/watch?v=" +
        elem.href.replace( /.*?[?&]v=(.*?)(?:&|$)/, "$1" );
    }
  }
);
}