Infinite scroll - loading more content when reaching bottm of document (or offset from bottom)

infiniteScroll.js

window.onscroll = function() {
  var offset = 100; //set offset from bottom
  var loading = false;
  var scrolledToOffset = document.documentElement.scrollTop + window.innerHeight + offset > document.documentElement.offsetHeight;
  if ( scrolledToOffset && !loading ) {
    function() {
      loading = true; //block running function more than once before finishing previous request
      //do something when reaching offset from bottom; e.g. load more content with AJAX
      loading = false; //pass this in callback function when using async call
    }
  }
};