Information, confirmation messagebox

<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" 
        OnClientClick="return confirmation();" onclick="Button1_Click"/>