treepanle beforeNodeDrop事件异步问题

在beforeNodeDrop事件中，弹出确认窗口之后，用户还没选择“是”/“否”，代码还会继续往下走，beforeNodeDrop = function beforeNodeDrop(e) {
        var curTree = e.tree;// 得到当前的tree
        var dropNode = e.dropNode;// 移动的节点
        var targetNode = e.target;// 目标节点
        var type = e.point;// 移动位置        Ext.Msg.confirm("系统提示", "你是否确定此操作?", function(_btn) {
          if (_btn == "yes") {
            ...............
          } else {
              return false;
          }
          }, this);          .......其他代码 
        
      }
用下面的修改，问题还是一样存在，事件不等待Ext.Ajax.request的返回状态，继续向下执行，
beforeNodeDrop = function beforeNodeDrop(e) {                                var curTree = e.tree;// 得到当前的tree                                var dropNode = e.dropNode;// 移动的节点                                var targetNode = e.target;// 目标节点                                var type = e.point;// 移动位置
                                // alert(Ext.util.JSON.encode(dropNode.attributes));
                                // alert(Ext.util.JSON.encode(targetNode.attributes));
                                var flag = false;
                                Ext.Ajax.request({
                                            url : '../common/Tree.jsp',
                                            method : 'post',
                                            params : {
                                                begin : "",
                                                end : ""
                                            },
                                            success : function(response, option) {
                                                var res_res = Ext.util.JSON.decode(response.responseText);
                                                if (res_res.success == true) {
                                                    flag = true;
                                                } else {
                                                    flag = false;
                                                }
                                            },
                                            failure : function(response, option) {
                                                alert("异步通讯失败，请与管理员联系！");
                                            }
                                        });
                                return flag;
                            }怎样实现，当移动节点是，会提示用户是否确定，等用户点击按钮以后在处理相应操作？？？？？？？