Add YouTube JS API support for embedded YouTube videos

Listener - YouTube .gtm.tag.html

<script>(function(){
/*
This script is an alternative to the 'Add JavaScript API support to all YouTube videos' 
setting in GTM's YT trigger.  GTM's YT trigger will not load the YT API if no videos are 
present at page load (it does add the enablejsapi param to dynanmically inserted videos, 
but it will not load the YT API js).  This script, on the other hand, should work in all cases.
*/
    
  if( window.YT ) return;
  
  var loadYoutubeApiOnce = (function(){
    
    var didIt;
    
    var scriptExists = function(){
      var scripts = document.getElementsByTagName("script");
      for( i=0; i < scripts.length; i++) {
        var src = scripts[i].getAttribute("src");
        if (src && (-1 < src.indexOf("//www.youtube.com/iframe_api") || -1 < src.indexOf("//www.youtube.com/player_api")))
          return true;
      }
    };
    
    return function(){
      if( didIt || window.YT || scriptExists() ) return (didIt=true);
      var j = document.createElement("script"),
          f = document.getElementsByTagName("script")[0];
      j.src = "https://www.youtube.com/iframe_api";
      j.async = true;
      f.parentNode.insertBefore(j,f);
      didIt=true;
    };
    
  })();


  var observeDOM = (function(){
      var MutationObserver = window.MutationObserver || window.WebKitMutationObserver,
          eventListenerSupported = window.addEventListener;

      return function(obj, callback){
          if( MutationObserver ){
              // define a new observer
              var obs = new MutationObserver(function(mutations, observer){
                  if( mutations[0].addedNodes.length )
                      callback();
              });
              // have the observer observe foo for changes in children
              obs.observe( obj, { childList:true, subtree:true });
              //return { stop : function(){ obs.disconnect()} };
          }
          else if( eventListenerSupported ){
              obj.addEventListener('DOMNodeInserted', callback, false);
              //return { stop : function(){ obj.removeEventListener( 'DOMNodeInserted', callback, false )} };
          }
      }
  })();

  // @func findYoutubeIframes
  // @desc Attach our YT listener once the API is loaded.  Enables JSAPI if it's not already on the URL. Note: this will cause the Youtube player to reload and "flash" on the page.
  var checkForYoutubeIframes = function() {
      var iframes, iframe, k, i, l = window.location;
      for (iframes = document.getElementsByTagName("iframe"), i = iframes.length; i--;) {
        iframe = iframes[i];
        if ( ! /youtube(-nocookie)?.com\/embed/i.test(iframe.src))
          continue;
        if( iframe.hasAttribute( 'data-gtm-fw-yt-listening' ) )
          continue;
        loadYoutubeApiOnce();
        iframe.setAttribute( 'data-gtm-fw-yt-listening', '' );
        if( ! iframe.src.match(/[?&]enablejsapi=1(&|$)/) ) {
          iframe.setAttribute('data-orig-src', iframe.src );
          iframe.src += 
            (iframe.src.indexOf('?')>-1?'&':'?') + 'enablejsapi=1'
            +'&origin='+encodeURIComponent( l.origin || l.protocol + "//" + l.hostname + (l.port ? ':' + l.port: '' ) )
        }
      }
  }
  
  checkForYoutubeIframes();
  
  observeDOM( document.body, checkForYoutubeIframes );

})()</script>