What are the ways to achieve partial refresh in ajax?

<script> 
setInterval("refreshTime()",1000); //每格1秒刷新一次 
funciton refreshTime() 
{ 
var dateObj = new Date(); 
time.innerHTML = dateObj.toLocaleDateString(); //刷新p里面的内容 
} 
</script> 
<p id=time> </p>

function doRef() 
{ 
var url = "xxx.aspx" 
var dateRequest = new ActiveXObject("Microsoft.XMLHTTP"); 
dateRequest.abort() ; 
dateRequest.open( "GET", url , true ); 
dateRequest.onreadystatechange = onSendSelf ; 
dateRequest.send() ; 
function onSendSelf() 
{ 
if( dateRequest.readyState != 4 ) 
{ 
return ; 
} 
var theDate = dateRequest.responseText ;//如果出现编码问题,可以在服务端escape一下,然后在这里使用unescape( responseText ) 
thep.innerHTML = theDate ; 
} 
} 
setInterval( doRef , 1000 ) ;//1秒刷新一次，有点快

<form id="form1" runat="server"> 
<asp:ScriptManager ID="ScriptManager1" runat="server"> 
</asp:ScriptManager> 
<br /> 
<asp:UpdatePanel ID="UpdatePanel1" runat="server"> 
<ContentTemplate> 
<asp:Timer ID="Timer1" runat="server" Interval="1000" OnTick="Timer1_Tick"> 
</asp:Timer> 
<asp:TextBox ID="TextBox1" runat="server"> </asp:TextBox> 
</ContentTemplate> 
</asp:UpdatePanel> 
</form>