asp.net给按钮添加删除确认

        if (!IsPostBack)
        {
            BtnDel.Attributes["onclick"] = "javascript:return window.confirm('你确定要删除该条数据吗？')";
        }

 <td vAlign="bottom" style="width: 75px">
                                    <asp:ImageButton ID="BtnDel" runat="server" ImageUrl="../images/an_sc.gif" OnClick="BtnDel_Click"/></td>