$(window).load(function () {
    var path = location.pathname;

    $('nav#mainmenu ul').children("li").each(function (i) {
        var Menupath = $(this).children('a').attr('href')
        var PathSlash = '/' + Menupath;

        if (path == PathSlash) {
            $(this).addClass('current');
        }
        else if ((path == '/') & (Menupath == 'Default.aspx')) {
            $(this).addClass('current');
        }
    });
});