Extjs ajax交付 提示等待信息

var myMask = new Ext.LoadMask(Ext.getBody(), {msg:"正在保存..."});

??? //catchScreen
??? function catchSrceen(){
??? ??????? myMask.show();
??? ??? Ext.Ajax.request({
??? ???
??? ??? ??? url:"CatchScreenServlet.do",
??? ??? ??? method:"post",
??? ??? ??? //wait:"正在获取远程桌面图片，请稍候...",
??? ??? ??? success:function(resq,conf){
??? ??? ??? ???
??? ??? ??? ??? Ext.getCmp("catchScreenId").body.update("<div><center><img <img? width=840 src='image/test.png'/></center></div>");
??? ??? ??? ??? //alert("success");
??? ??? ??? }
??? ??? })
??? }