以下是代码：

 <script type="text/javascript">
        $(function(){
            $("#btnOk").click(function(){
              
                $.ajax({
                    url: "/ajax/CheckInGroup.ashx",
                    type: "GET",
                    data: "groupID=" + $("#ddlGroups").val() + "&userID=<%=userID %>",
                    success: function(msg){
                        if (msg == "No")
                        {
                            alert("对不起,您已经存在于组中,不能重复添加!");
                        }
                        else
                        {
                        }                     
                    }
                });
            });                          
        });
    </script>

我想如果提示"对不起,您已经存在于组中,不能重复添加!"的时候，那么按钮的单击事件返回值为false,表示不提交,否则的话就提交!返回true和false的代码应该怎么写了？请大家帮忙，先谢过！