sticky-menu-bar.js

/**
     * Makes the filter bar sticky when it reaches the top of the screen by scrolling, and un-sticks it if you scroll above the screen.
     * Also fills in the primary nav bar when the filter bar becomes sticky.
     */
    function stickyFilterBar() {
        window.filterBarIsFixed = false;
        var filterSortBar = document.querySelector(".filter-sort-bar"); //Parent element
        if (filterSortBar !== null) {
            var topButtonBar = document.querySelector(".top-button-bar");
            var topButtonBarHeight = jQuery(topButtonBar).height();

            var primaryNavHeader = document.getElementById("header");
            var primaryNavHeight = jQuery(primaryNavHeader).height();
            var offsetTop = topButtonBar.offsetTop - primaryNavHeight; //The height at which the filter bar is just below the navbar

            window.addEventListener("scroll", function () {
                //console.log("ScrollY: " + window.scrollY);
                //console.log("Offset: " + offsetTop);
                var fixedClass = " fixed-to-top";
                if ((window.scrollY >= offsetTop) && ( !window.filterBarIsFixed )) {
                    window.filterBarIsFixed = true;
                    filterSortBar.style.position = "fixed";
                    filterSortBar.style.zIndex = "2";
                    filterSortBar.style.top = primaryNavHeight + "px";

                    //When the bar becomes fixed, need to add to the top margin of next sibling so that it doesn't slide under
                    //the fixed filter bar.
                    filterSortBar.nextElementSibling.style.marginTop = topButtonBarHeight + "px";

                    //Fill in the background color of the primary nav
                    primaryNavHeader.style.backgroundColor = "#332b2a";
                }
                if ((window.scrollY < offsetTop) && ( window.filterBarIsFixed )) {
                    window.filterBarIsFixed = false;
                    filterSortBar.style.position = "static";
                    filterSortBar.style.zIndex = "initial";
                    filterSortBar.nextElementSibling.style.marginTop = "0px";

                    //Change back to transparent the background color of the primary nav
                    primaryNavHeader.style.backgroundColor = "transparent";
                }
            })
        }
    }