div随着屏幕滚动而滚动

      $(document).ready(function () {
        var menuYloc = $("#leftmenu").offset().top; //此ID为随着屏幕滚动div的ID
        $(window).scroll(function () {
          var offsetTop = menuYloc + $(window).scrollTop() + "px";
          $("#leftmenu").animate({
            top: offsetTop
          }, {
            duration: 600,
            queue: false
          }); //此ID为随着屏幕滚动div的ID
        });
      });