https://mandarte.nl/media/templates/site/cassiopeia/js/mod_menu/menu-metismenu.js?a7d916

1/**
2 * @package     Joomla.Site
3 * @subpackage  Templates.cassiopeia
4 * @copyright   (C) 2020 Open Source Matters, Inc. <https://www.joomla.org>
5 * @license     GNU General Public License version 2 or later; see LICENSE.txt
6 * @since       4.0.0
7 */
8
9document.querySelectorAll('ul.mod-menu_dropdown-metismenu').forEach(menu => {
10  const mm = new MetisMenu(menu, {
11    triggerElement: 'button.mm-toggler'
12  }).on('shown.metisMenu', event => {
13    function mmClick(e) {
14      if (!event.target.contains(e.target)) {
15        mm.on('hidden.metisMenu', () => {
16          window.removeEventListener('click', mmClick);
17        });
18        mm.hide(event.detail.shownElement);
19      }
20    }
21    window.addEventListener('click', mmClick);
22  });
23});