jQuery设置div一直在页面顶部显示的方法

jQuery部分

<script src="JS/jquery-1.8.3.js" type="text/javascript"></script> 
<script type="text/javascript"> 
$(function () { 
var elm = $('#pordAttr'); 
var startPos = $(elm).offset().top; 
$.event.add(window, "scroll", function () { 
var p = $(window).scrollTop(); 
$(elm).css('position', ((p) > startPos) ? 'fixed' : 'static'); 
$(elm).css('top', ((p) > startPos) ? '0px' : ''); 
}); 
}); 
</script>

HTML部分

<div id="pordAttr"> 
<input type="text" value="奇异果" id="txtSearchImage" runat="server" /> 
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" /> 
</div>