docdash/static/scripts/collapse.js

function hideAllButCurrent(){
    //by default all submenut items are hidden
    //but we need to rehide them for search
    document.querySelectorAll("nav > ul").forEach(function(parent) {
        if (parent.className.indexOf("collapse_top") !== -1) {
            parent.style.display = "none";
        }
    });
    document.querySelectorAll("nav > ul > li > ul li").forEach(function(parent) {
        parent.style.display = "none";
    });
    document.querySelectorAll("nav > h3").forEach(function(section) {
        if (section.className.indexOf("collapsed_header") !== -1) {
            section.addEventListener("click", function(){
                if (section.nextSibling.style.display === "none") {
                    section.nextSibling.style.display = "block";
                } else {
                    section.nextSibling.style.display = "none";
                }
            });
        }
    });
    
    //only current page (if it exists) should be opened
    var file = window.location.pathname.split("/").pop().replace(/\.html/, '');
    document.querySelectorAll("nav > ul > li > a").forEach(function(parent) {
        var href = parent.attributes.href.value.replace(/\.html/, '');
        if (file === href) {
            if (parent.parentNode.parentNode.className.indexOf("collapse_top") !== -1) {
                parent.parentNode.parentNode.style.display = "block";
            }
            parent.parentNode.querySelectorAll("ul li").forEach(function(elem) {
                elem.style.display = "block";
            });
        }
    });
}

hideAllButCurrent();