https://rci.fm/modules/contrib/stickynav/js/stickynav.js?v=1.x

1/**
2 * @file
3 * Contains JavaScript making the eleements stick.
4 */
5
6(function ($, Drupal, drupalSettings) {
7  'use strict';
8
9  /**
10   * Attach the stickiness to the element in selector.
11   *
12   * @type {Drupal~behavior}
13   *
14   * @prop {Drupal~behaviorAttach} attach
15   *   Make the element in selector sticky.
16   */
17  Drupal.behaviors.stickynav = {
18    breakpoint: 0,
19    compensation: 0,
20    originalPadding: 0,
21    attach: function (context) {
22      var selector = drupalSettings.stickynav.selector;
23      // Only getting the first elmenet in the dom.
24      var $menu = $(selector).once('stickynav').eq(0);
25      var offset = 0;
26      if ($menu.length) {
27        // Save original padding on top. 0 timeout to get correct padding.
28        setTimeout(function () {
29          Drupal.behaviors.stickynav.originalPadding = $('body').css('paddingTop');
30        }, 100);
31        offset += parseInt(drupalSettings.stickynav.offsets.custom_offset);
32        offset = offset || 0;
33        $(drupalSettings.stickynav.offsets.selector).each(function () {
34          offset += $(this).outerHeight();
35        });
36        Drupal.behaviors.stickynav.breakpoint = $menu.offset().top - offset;
37        // We need to compensate the element so that the content does not jump up.
38        Drupal.behaviors.stickynav.compensation = $menu.outerHeight();
39        $(window).scroll(function () {
40          if ($(window).scrollTop() > Drupal.behaviors.stickynav.breakpoint) {
41            $menu.addClass('stickynav-active');
42            if (offset) {
43              $menu.css({top: offset + 'px'});
44            }
45            $('body').css('padding-top', Drupal.behaviors.stickynav.compensation);
46          }
47          else {
48            $menu.removeClass('stickynav-active');
49            $menu.css({top: ''});
50            $('body').css('padding-top', Drupal.behaviors.stickynav.originalPadding);
51          }
52        });
53      }
54    }
55  };
56})(jQuery, Drupal, drupalSettings);