geek-cookbook/manuscript/extras/javascript/auto-expand-nav.js

document.addEventListener("DOMContentLoaded", function() {
    load_navpane();
});

function load_navpane() {
    var width = window.innerWidth;
    if (width <= 1200) {
        return;
    }

    var nav = document.getElementsByClassName("md-nav");
    for(var i = 0; i < nav.length; i++) {
        if (typeof nav.item(i).style === "undefined") {
            continue;
        }

        if (nav.item(i).getAttribute("data-md-level") && nav.item(i).getAttribute("data-md-component")) {
            nav.item(i).style.display = 'block';
            nav.item(i).style.overflow = 'visible';
        }
    }

    var nav = document.getElementsByClassName("md-nav__toggle");
    for(var i = 0; i < nav.length; i++) {
       nav.item(i).checked = true;
    }
}