后端：页面需继承ICallbackEventHandler
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{ string strRefrence = string.Empty;
strRefrence = Page.ClientScript.GetCallbackEventReference(this, "arg", "ReceiveDataFromServer", "context"); // 这里ReceiveDataFromServer为客户端接收回调结果的JS方法，含一个传入参数 string strCallBack = string.Empty;
strCallBack = "function CallBackToTheServer(arg, context) {" + strRefrence + "};"; Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "CallBackToTheServer", strCallBack, true); // CallBackToTheServer，JS方法，发出回调请求 } }
#region ICallbackEventHandler Members private string strTimeFormat; public string GetCallbackResult()
{
if (strTimeFormat != "" && strTimeFormat == "")
{
return DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss（12小时制）");
}
else
{
return DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss（24小时制）");
}
} public void RaiseCallbackEvent(string eventArgument)
{
strTimeFormat = eventArgument;
} #endregion
前端：
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script>
function ReceiveDataFromServer(valueReturnFromServer) {
document.getElementById("ServerTime").innerHTML = valueReturnFromServer;
} function GetServerTime(format) {
CallBackToTheServer(format, "");
} </script>
<title></title>
</head>
<body>
<form id="form1" runat="server"> <div>
<asp:Button ID="btnShow12" runat="server" Text="获取服务器时间（12小时制）" OnClientClick="javascript:GetServerTime(12);return false;" /><br />
<asp:Button ID="btnShow24" runat="server" Text="获取服务器时间（24小时制）" OnClientClick="javascript:GetServerTime(24);return false;" /><br />
<br />
<span id="ServerTime"><%= DateTime.Now.ToString("yyyy-MM-dd HHHH:mm:ss") %></span>
</div>
</form>
</body>
</html>