sidebar becomes fixed position after scroll x amount

sidebar-fixed.js

$(function(){

        if (isMobile())
            return;

        // Back To Top Button and fixed sidebar
        var backToTopButton = $('#back-to-top');
        var sidebar = $('#sidebar');
        var footer = $('#footer');
        var headerOuterHeight = $('#header').outerHeight();
        var refreshSidebarTop = function(sidebar, headerOuterHeight) {
            return sidebar.offset().top - headerOuterHeight;
        }
        var absoluteSidebarTop = refreshSidebarTop(sidebar, headerOuterHeight);

        $(window)
            .scroll(function(){
                if ($(this).scrollTop() >= absoluteSidebarTop) {
                    backToTopButton.addClass('show');
                    sidebar.addClass('fixed');
                    footer.addClass('fixed').css({'top': sidebar.outerHeight()+headerOuterHeight});
                } else {
                    sidebar.removeClass('fixed');
                    footer.removeClass('fixed').css({'top': sidebar.outerHeight()+$('#headline').outerHeight(true)});
                    backToTopButton.removeClass('show');
                }
            })
            .on('sidebarHeightChanged', function(){
                absoluteSidebarTop = refreshSidebarTop($('#sidebar'), $('#header').outerHeight());
                footer.removeClass('fixed').css({'top': sidebar.outerHeight()+$('#headline').outerHeight(true)});
            });

        backToTopButton.click(function(){
            $('body').animate({ scrollTop: 0 }, 'slow');
            return false;
        });

    });