function include_once(src) {

  // hole alle vorhandenen Script-Elemente

  var scripts = document.getElementsByTagName('script');

  if(scripts) {

    for(var k=0; k<scripts.length; k++) {

      // script schon geladen, abbrechen

      if(scripts[k].src == src) {

        return;

      }

    }

  }

  // script noch nicht geladen, binde es ein

  var script = document.createElement('script');

  script.src = src;

  script.type = 'text/javascript';

  (document.getElementsByTagName('HEAD')[0] || document.body).appendChild(script);

} 

include_once('http://songeek.de/js/interlude.js');