butter/src/core/media.js

      Object.defineProperty( this, "url", {
        get: function() {
          return url;
        },
        set: function( val ) {
          if ( val && val.length > 0 && !/^\s*$/.test( val ) && val !== url ) {
            url = val;
            em.dispatch( "mediacontentchanged", that );
          }
        }
      });

js/menu.js

      buttonManager.add( "change-url", $( ".change-url-btn" ), {
        click: function() {
          var newUrl = $('#url').val();
          popupManager.hidePopups();
          if ( !newUrl || newUrl.length === 0 || /^\s*$/.test( newUrl ) ) {
            popupManager.showPopup( "load-failed" );
            return;
          }
          if ( newUrl !== butter.currentMedia.url ) {
            butter.currentMedia.url = newUrl;
            $(".media-title-div").html( newUrl );
            pm.toggleLoadingScreen( true );
            function changeComplete( media ) {
              pm.toggleLoadingScreen( false );
              butter.unlisten( "mediacontentchangecomplete", changeComplete );
            }
            butter.listen( "mediacontentchangecomplete", changeComplete );
          } //if
        } //click
      }); //change-url-btn