Coolite 

<ext:Window ID="Window1" runat="server" CloseAction="Hide" Collapsible="true" icon="Application" Title="Title">
 <Listeners>
   <Hide Handler="RelayEvent('hide','')" />
   <Move Handler="RelayEvent('move','')" />
 </Listeners>
</ext:Window>

Partial Class _Default
  Inherits System.Web.UI.Page
  Implements ICallbackEventHandler

Private _callbackArg As String

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
  Dim cbReference As String
  cbReference = Page.ClientScript.GetCallbackEventReference(Me, "arg", "ReceiveServerData", "context")
  Dim callbackScript As String
  callbackScript = "function RelayEvent(arg, context)" & "{" & cbReference & "; }"
  Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "RelayEvent", callbackScript, True)
End Sub 

Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult
  Select Case _callbackArg
  Case "hide"
    Return "Hidden"
  Case "move"
    Return "Moved"
  Case Else
    Return _callbackArg
  End Select
End Function

Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent
   _callbackArg = eventArgument
End Sub
End Class

<script type="text/javascript">
function ReceiveServerData(arg, context)
{
  document.getElementById('Text1').innerText = arg;
}