https://www.natura2000.fr/modules/contrib/scroll_top_button/js/scroll.top.button.js?v=1.x

1(function ($, window, Drupal) {
2
3    Drupal.behaviors.scrollTopButton = {
4      attach: function (context, settings) {
5
6        var button_text = drupalSettings.button_text;
7        var button_style = drupalSettings.button_style;
8        var button_animation = drupalSettings.button_animation;
9        var button_animation_speed = parseInt(drupalSettings.button_animation_speed);
10        var scroll_distance = parseInt(drupalSettings.scroll_distance);
11        var scroll_speed = parseInt(drupalSettings.scroll_speed);
12
13        var element_name = 'scrollTopButton-' + button_style;
14
15        if (button_style == 'image') {
16          button_text = '';
17        }
18
19        var $element = $('<a/>', {id: element_name, href: '#', class:'scroll-top-button'});
20
21        if ($('#' + element_name).length === 0) {
22          $element.appendTo('body');
23        }
24
25        $element.html(button_text);
26
27        var animationIn = 'show';
28        var animationOut = 'hide';
29        var animationSpeed = 0;
30        var buttonVisible = false;
31
32        // set animation for the button
33        if (button_animation == 'fade') {
34          animationIn = 'fadeIn';
35          animationOut = 'fadeOut';
36          animationSpeed = button_animation_speed;
37        }
38
39        if (button_animation == 'slide') {
40          animationIn = 'slideDown';
41          animationOut = 'slideUp';
42          animationSpeed = button_animation_speed;
43        }
44
45        $(window).scroll(function () {
46            if ($(window).scrollTop() > scroll_distance) {
47                if (!buttonVisible) {
48                    $element[animationIn](animationSpeed);
49                    buttonVisible = true;
50                }
51            } else {
52                if (buttonVisible) {
53                    $element[animationOut](animationSpeed);
54                    buttonVisible = false;
55                }
56            }
57        });
58
59        // Scroll to top after click on button
60        $element.click(function (event) {
61          event.preventDefault();
62
63            $('html, body').animate({ scrollTop: 0}, scroll_speed, 'linear');
64        });
65
66      }
67    };
68
69  })(jQuery, window, Drupal);