div随着屏幕滚动而滚动

<script type="text/javascript">
$(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
});
});
</script>