using javascript with update panel

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C#

ASP.NET

Javascript

Ajax

Google

hi,

this is my code

<form runat="server">
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<contenttemplate>
<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">
<asp:ListItem>--Selectione--
<asp:ListItem>Qualitas
<asp:ListItem>ABHS




<asp:UpdatePanel ID="UpdatePanel3" runat="server">
<contenttemplate>
<div id="mapcanva" runat="server">
<asp:Literal ID="Literal1" runat="server">



</form>

<script src="https://maps.googleapis.com/maps/api/js?v=3.exp"></script>
   <script>

       function initialize() {
           var myLatlng = new google.maps.LatLng(33.596854, -7.604025);
           var mapOptions = {
               zoom: 16,
               center: myLatlng
           };

           var map = new google.maps.Map(document.getElementById('mapcanva'), mapOptions);

           var contentString = 'Qualitas Environmental Solutions';

           var infowindow = new google.maps.InfoWindow({
               content: contentString
           });

           var marker = new google.maps.Marker({
               position: myLatlng,
               map: map,
               title: 'Qualitas'
           });
           google.maps.event.addListener(marker, 'click', function () {
               infowindow.open(map, marker);
           });
       }

       google.maps.event.addDomListener(window, 'load', initialize);

   </script>

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
       {
           if (DropDownList1.Text=="ABHS")
           {
               mapcanva.Visible = false;


           }
           else if (DropDownList1.Text == "Qualitas")
           {
               mapcanva.Visible = true;

           }
       }

when i selected item "ABHS" the div set visible to false but when i selecte "Qualitas" the div set visible to falsebut the map don't aprea i dont know why plz help me