JQuery Detect the browser window top and change CSS on page

JQuery Detect the browser window top and change CSS on page

 var t = $("#nav2").offset().top;

    $(document).scroll(function() {
        if ($(this).scrollTop() > t)
        {
            $('#nav2').css('position', 'fixed');
            $('#nav2').css('top', '0');
        }
        else
        {
            $('#nav2').css('position', 'relative');
        }
    });