Highlight Targeted Items with Scroll Limit

   // limit scroll call for performance
   var scrollHandling = {
    allow: true,
    reallow: function() {
      scrollHandling.allow = true;
    },
    delay: 500 //(milliseconds) adjust to the highest acceptable value
  };

// filter function for finding data-scrollto element matching class
$.fn.filterByData = function (name, value) {
  return this.filter(function () {
    return $(this).data(name) === value;
  });
};

if ($('.side_nav_wrapper').length > 0) { // check for side_nav_wrapper
  $(window).on('scroll', function () {
       if(scrollHandling.allow) { // call scroll limit
      var halfWay = $(window).height() / 2; // get half height of window
      $('.sectionAnchor').each(function () { // check each section anchor
          var distance = $(this).offset().top - halfWay; // check when halfway from top
          if ($(window).scrollTop() >= distance) {
            $('.pageScroller').removeClass('active');
            var classString = $(this).attr('class');
            if (classString) {
                  //Get first class from class string
                  var target = classString.split(' ')[0];
                  //Find anchors and filter by data-scrollto == our class name
                  var navItem = $('.pageScroller').filterByData('scrollto', target);

                  navItem.addClass('active');
                }
              }
            });
        } // end scorll handling limit
  }); // end window scroll
} // end check for side_nav_wrapper