code: function scrollSidebar(event) {
              if (event.handled !== true) {
                  var scrollTop = $window.scrollTop(),
                      maxScrollTop = $document.height() - $window.height();
                  if (scrollTop >= 0 && prevScrollTop >= 0 && scrollTop <= maxScrollTop && prevScrollTop <= maxScrollTop) {  // for Mac scrolling
                      $sidebar.scrollTop($sidebar.scrollTop() + (scrollTop - prevScrollTop));
                  }
                  prevScrollTop = scrollTop;
                  event.handled = true;
              }
              else {
                  return false;
              }
          }
docs: Synchronize sidebar scroll