Angular 1.5 - Calls a method when user scrolls to bottom

on-scroll-to-bottom.directive.js

function OnScrollToBottom() {
  'ngInject';

  let spacing = 40;

  return {
    
    restrict: 'A',
    link: function (scope, element, attrs) {
      const fn = attrs.onScrollToBottom,
          clientHeight = element[0].clientHeight;

      element.on('scroll', function (e) {
        const el = e.target;

        if ((el.scrollHeight - el.scrollTop) <= clientHeight + spacing) {
          scope.$apply(fn);
        }
      });
    }
    
  }; 
}

export default OnScrollToBottom;

You can call it like so:
<div class='viewport' on-scroll-to-bottom="$ctrl.loadMorePosts()">