https://www.brethrenarchive.org/Scripts/menu-toggle.js

1// Vanilla replacement for Foundation's responsiveToggle plugin: the
2// title-bar hamburger (data-toggle="main-menu") shows/hides the top-bar
3// menu on small screens; at the medium breakpoint (40em, same as the old
4// Foundation setting) the menu is always visible.
5(function () {
6    'use strict';
7    var menu = document.getElementById('main-menu');
8    if (!menu) return;
9
10    var mq = window.matchMedia('(min-width: 40em)');
11
12    function applyBreakpoint() {
13        menu.style.display = mq.matches ? '' : 'none';
14    }
15
16    var toggles = document.querySelectorAll('[data-toggle="main-menu"]');
17    for (var i = 0; i < toggles.length; i++) {
18        toggles[i].addEventListener('click', function () {
19            if (mq.matches) return; // always visible on medium+
20            menu.style.display = (menu.style.display === 'none') ? '' : 'none';
21        });
22    }
23
24    if (mq.addEventListener) mq.addEventListener('change', applyBreakpoint);
25    else mq.addListener(applyBreakpoint); // older Safari
26    applyBreakpoint();
27})();