jquery 设置div在浏览器的位置

<script type="text/javascript">

var offset = $("#health_alert").offset();

var alert_top = offset.top;

var window_height =$(window).height();

var alert_hight = $("#health_alert").outerHeight();

var alert_top = ( window_height - alert_hight )/ 2;

$("#health_alert").offset({ top: alert_top});

//alert(alert_hight);

</script>

http://api.jquery.com/height/

http://api.jquery.com/offset/