Display Confirmation BOX yes no on ASP.NET Button Click VS 2008 VB.net

 <script type="text/javascript">
        function confirmation() {
            if (confirm('are you sure you want to delete ?')) {
            return true;
            }else{
            return false;
            }
        }
    </script> 

<asp:button id="Button1" runat="server" text="Button" xmlns:asp="#unknown">
OnClientClick="return confirmation();" onclick="Button1_Click"/></asp:button>

Response.Write("<script>return confirmation();" </script>");

<asp:button id="btnDelete" runat="server" text="Delete" onclientclick="return confirm('Do you want to delete this record?');" xmlns:asp="#unknown" />

<script type="text/javascript">
        function confirmation() {
            if (confirm('are you sure you want to delete ?')) {
            return true;
            }else{
            return false;
            }
        }
    </script>