https://greppa.nu/download/18.73587d8a198eca95c9d6584e/1758091334158/gre-scrollpage.js

1svDocReady(function() {
2
3   $ = $svjq;
4
5   var height = 600;
6
7   $('#scrollBall').click(function(e) {
8      e.preventDefault();
9      if (document.documentElement.clientHeight + $(document).scrollTop() >= document.body.offsetHeight ) {
10         $('body,html').animate({
11            scrollTop: 0
12         }, 800);
13         height = 600;
14      } else {
15         $('body,html').animate({
16            scrollTop: height
17         }, 800);
18         height = height + 600;
19      }
20   });
21
22
23
24   $(document).scroll(function() {
25      if (document.documentElement.clientHeight + $(document).scrollTop() >= document.body.offsetHeight ) {        
26         $('#scrollBall').removeClass('gre-scroll-down').addClass('gre-scroll-up');
27      } else {
28         $('#scrollBall').removeClass('gre-scroll-up').addClass('gre-scroll-down');
29      }
30   });
31
32});