https://www.colibris-nancy.fr/wp-content/themes/generatepress/assets/js/back-to-top.js

1( function() {
2	'use strict';
3
4	// Feature Test
5	if ( 'querySelector' in document && 'addEventListener' in window ) {
6		var goTopBtn = document.querySelector( '.generate-back-to-top' );
7
8		var trackScroll = function() {
9			var scrolled = window.pageYOffset;
10			var coords = goTopBtn.getAttribute( 'data-start-scroll' );
11
12			if ( scrolled > coords ) {
13				goTopBtn.classList.add( 'generate-back-to-top__show' );
14			}
15
16			if ( scrolled < coords ) {
17				goTopBtn.classList.remove( 'generate-back-to-top__show' );
18			}
19		};
20
21		// Function to animate the scroll
22		var smoothScroll = function( anchor, duration ) {
23			// Calculate how far and how fast to scroll
24			var startLocation = window.pageYOffset;
25			var endLocation = document.body.offsetTop;
26			var distance = endLocation - startLocation;
27			var increments = distance / ( duration / 16 );
28			var stopAnimation;
29
30			// Scroll the page by an increment, and check if it's time to stop
31			var animateScroll = function() {
32				window.scrollBy( 0, increments );
33				stopAnimation();
34			};
35
36			// Stop animation when you reach the anchor OR the top of the page
37			stopAnimation = function() {
38				var travelled = window.pageYOffset;
39				if ( travelled <= ( endLocation || 0 ) ) {
40					clearInterval( runAnimation );
41					document.activeElement.blur();
42				}
43			};
44
45			// Loop the animation function
46			var runAnimation = setInterval( animateScroll, 16 );
47		};
48
49		if ( goTopBtn ) {
50			// Show the button when scrolling down.
51			window.addEventListener( 'scroll', trackScroll );
52
53			// Scroll back to top when clicked.
54			goTopBtn.addEventListener( 'click', function( e ) {
55				e.preventDefault();
56
57				if ( generatepressBackToTop.smooth ) {
58					smoothScroll( document.body, goTopBtn.getAttribute( 'data-scroll-speed' ) || 400 );
59				} else {
60					window.scrollTo( 0, 0 );
61				}
62			}, false );
63		}
64	}
65}() );