CODE EXAMPLE FOR JAVASCRIPT

if window width jquery then display a div at scroll

function updateContainer() {
    $(window).scroll(function() {

        if ( $(window).width() > 960 ) {

            if( $(window).scrollTop() > 40 && $(document).height() - $(window).height() > 79 ) { // scroll bug appears if 78 or lower
                add_desktop();
            } else if ($(window).scrollTop() <= 40 ) {
                remove_desktop();
            }

        } else {

            if( $(window).scrollTop() > 40 && $(document).height() - $(window).height() > 160 ) {
                add_mobile();
            } else if ($(window).scrollTop() <= 40 ) {
                remove_mobile();
                //alert (winwidth);
            }

        }

    });

}