extjs4.1 树形菜单问题

JScript code

var Root = Ext.create("Ext.tree.Panel");Ext.Ajax.timeout = 60 * 60 * 60;Ext.data.Connection.timeout = 60 * 60 * 60;Ext.data.proxy.Server.timeout = 60 * 60 * 60;var treeNode = [];var webNode = {    text: "网站相关",    children: [        {            text: "网站首页",            leaf: true,            id: "index"/*,            handler: function () {                window.open("/", "_blank");            }*/        }, {            text: "网站基本信息",            leaf: true,            id: "basicInfo"/*,            handler: function () {                //MainPanel.add(createPanel()).show();                //MainPanel.doLayout();            }*/        }    ]};treeNode.push(webNode);var cmsNode = {    text: "信息网",    children: [        {            text: "网站首页",            leaf: true,            id: "index"/*,            handler: function () {                window.open("/", "_blank");            }*/        }, {            text: "文章管理",            leaf: true,            id: "ArticleManage"/*,            handler: function () {                //MainPanel.add(createArticlePanel()).show();                //MainPanel.doLayout();            }*/        }    ]};treeNode.push(cmsNode);var store = Ext.create('Ext.data.TreeStore', {    root: {        expanded: true,        children: treeNode    }});Root = Ext.create("Ext.tree.Panel", {    title: "功能列表",    rootVisible: false,    store: store,    listeners: {        itemclick: function (view, record) {            if (record.raw.handler) {                record.raw.handler();            } else {                ExtAlert("该节点未注册点击事件");            }        }    }});

上面定义了两个菜单，每个菜单有两个子节点
现在的问题是
第一次展开一个父节点时，不管展开哪一 个，都没有错误
第二次展开时，不管展开哪一个，都报错a[b] is undefined

求指点

[解决办法]
我来了，给我吧