AsyncFileUpload ClientUploadStarted event in asp.net ajax

Ajax AsyncFileUpload OnClientUploadStarted
UsingOnClientUploadStarted.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

<!DOCTYPE html>
<script runat="server">
    protected void AsyncFileUpload1_UploadComplete(object sender, AjaxControlToolkit.AsyncFileUploadEventArgs e)
    {
        string filePath = Request.PhysicalApplicationPath+ "Upload\\" + AsyncFileUpload1.PostedFile.FileName;
        AsyncFileUpload1.SaveAs(filePath);
    }    
</script>
<script type="text/javascript">
    function showConfirmation() {
        document.getElementById('Label2').innerText = 'upload complete.';
    }
    function showUploadStartMessage(sender, args) {
        document.getElementById('Label1').innerText = args.get_fileName()+' upload started...';
    }
    function showUploadError(sender,args) {
        document.getElementById('Label2').innerText = args.get_errorMessage();
    }
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Ajax AsyncFileUpload OnClientUploadStarted  - How to use OnClientUploadStarted</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:SlateBlue; font-style:italic;">Ajax AsyncFileUpload Example: How To Use OnClientUploadStarted</h2>
        <hr width="575" align="left" color="MediumBlue" />
        <asp:ScriptManager 
            ID="ScriptManager1"
            runat="server"
            >
        </asp:ScriptManager>
        <br />
        <cc1:AsyncFileUpload 
            ID="AsyncFileUpload1" 
            runat="server" 
            OnUploadedComplete="AsyncFileUpload1_UploadComplete"
            OnClientUploadComplete="showConfirmation"
            OnClientUploadError="showUploadError"
            OnClientUploadStarted="showUploadStartMessage"
            CompleteBackColor="SkyBlue"
            UploaderStyle="Traditional"
            BackColor="IndianRed"
            ErrorBackColor="Salmon"
            />
        <br />
        <asp:Label 
            ID="Label1"
            runat="server"
            Font-Names="Comic Sans MS"
            ForeColor="SeaGreen"
            Font-Size="X-Large"
            Font-Italic="true"
            Font-Bold="true"
            >
        </asp:Label>
        <br />
        <asp:Label 
            ID="Label2"
            runat="server"
            Font-Names="Comic Sans MS"
            ForeColor="DarkSeaGreen"
            Font-Size="X-Large"
            Font-Italic="true"
            Font-Bold="true"
            >
        </asp:Label>
    </div>
    </form>
</body>
</html>
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