Ajax Js倒计时执行后台方法

HTML代码

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head runat="server">
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<title>Untitled Page</title>
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function hello()
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{
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BeginMessage();
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var t=setTimeout("endMessage('计时结束 5 seconds!')",5000)
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}
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function endMessage(msg)
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{
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PageMethods.Msg(msg,updateMessages);
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}
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function BeginMessage()
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{
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PageMethods.Msg("计时开始",updateMessages);
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}
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function updateMessages(result)
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{
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$get("lbl").innerHTML =result;
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}
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</script>
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</head>
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<body>
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<form id="form1" runat="server">
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<asp:ScriptManager ID="ScriptManager1" EnablePageMethods="true" runat="server" />
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<div>
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<asp:Label ID="lbl" runat="server" Text="Label"></asp:Label
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><input id="Button1" type="button"
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value="开始" onclick="hello()" />
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</div>
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</form>
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</body>
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</html>
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后台代码

Default.aspx.cs