bottom_of_blog_tracking.html

<script>
  
  (function(dataLayer, $) {
    
    var reachedBottom = false;
  	//returns true if view is at or below element
  	function scrolledToBottom(elem) {
      	var $elem = $(elem);
      	if ($elem.length > 0) {
        	var $window = $(window);

        	var docViewTop = $window.scrollTop();
        	var docViewBottom = docViewTop + $window.height();

        	var elemTop = $elem.offset().top;
        	var elemBottom = elemTop + $elem.height();
    
        	return (elemBottom <= docViewBottom);
      } else {
        	return false;
      }
  }
  
   	//sends an event if view is at or below element
    $(document).scroll(function() {
    	reachedBottom = scrolledToBottom('#waypoints_identifier');
    	
      	if (reachedBottom) {
        	dataLayer.push({'event': 'scrolled-to-bottom'});
      		$(document).off('scroll');
      	}	
    });
  
  })(window.dataLayer || [], window.$ || window.jQuery);
  
</script>

I think the problem is this line: 26: reachedBottom = scrolledToBottom('#waypoints_identifier');

waypoints_identifier is not an element that exists in the page.