https://www.suidou-setubi.com/blog/wp-content/themes/works/js/scroll.js

1var up_timer
2
3function getPosition(){
4	yoko = document.body.scrollLeft || document.documentElement.scrollLeft;
5	tate = document.body.scrollTop  || document.documentElement.scrollTop;
6
7}
8
9function pageup(x,y){
10	if(up_timer) clearTimeout(up_timer);
11	if(y >= 1){
12		getPosition();
13		var divisionY = (tate-(tate/7));
14		var Y = Math.floor(divisionY);
15		window.scrollTo(yoko,Y);
16		up_timer = setTimeout("pageup("+yoko+","+Y+")",10);
17	}else{
18		window.scrollTo(yoko,0);
19		clearTimeout(up_timer);
20	}
21}
22
23function scrollup(){
24		getPosition();
25		pageup(yoko,tate)
26}