https://www.preiselbauer.de/wp-content/themes/noto-simple/js/main.js?ver=201811

1/**
2 * File main.js.
3 *
4 * Theme's custom functions.
5 */
6
7var toTopBtn = document.getElementById('back-to-top');
8var scroll = new SmoothScroll('a[href*="#"]');
9
10/**
11 * Scroll event.
12 */
13window.onscroll = function() {
14	showToTopButton();
15}
16
17/**
18 * Scroll event callback to display/hide back-to-top button.
19 */
20function showToTopButton() {
21	if (document.body.scrollTop > 500 ||
22		document.documentElement.scrollTop > 500) {
23		toTopBtn.classList.add('shown');
24
25	} else {
26		toTopBtn.classList.remove('shown');
27	}
28}