content/_includes/footer_scripts.html

<script>

    function addCollapsed(el) {
        el.classList.add('collapsed');
    }

    function toggleCollapsed(ev) {
        ev.target.parentNode.classList.toggle('collapsed');
        ev.preventDefault();
    }

    function addClickEvent(el) {
        console.log(el);
        el.addEventListener('click', toggleCollapsed);
    }

    document.querySelectorAll('.sidebar-node').forEach(addCollapsed);
    document.querySelectorAll('.sidebar-node > a').forEach(addClickEvent);

    // preserve expand/collapse across page navigation
    var el = document.getElementById("v3-0");
    console.log(el);
    el.classList.remove("collapsed");
</script>