Loading gif Image on i frame loading

<script type="text/javascript">
        function hideLoading() {
            document.getElementById('divLoading').style.display = "none";
            document.getElementById('divFrameHolder').style.display = "block";
        }
    </script>

 <div id="divLoading">

        <asp:Image ID="imgloading" runat="server" ImageUrl="Images/preload.gif" />
    </div>
    <div id="divFrameHolder" style="display:none">
        <iframe src="LoadData.aspx" onload="hideLoading()" frameborder="1" scrolling="auto" width="650px;" height="500px">
     
        </iframe>
    </div>