Ext.MessageBox.confirm无反应

<script type="text/javascript" src="${path}/extjs/ext-all.js"></script>

<script type="text/javascript">
function exitSystem() {

Ext.MessageBox.confirm('信息','确定要退出医药管理系统吗?', function (select) {
if (select == 'yes') {
window.open('', '_self', '');
window.close();
}
});
}
</scripti>
<a href="javascript:exitSystem();" title="退出"></a>为什么点击这个没有反应
<link rel="stylesheet" type="text/css" href="${path}/ext/resources/css/ext-all.css"/>
<script type="text/javascript" src="${path}/ext/ext-all.js"></script>
<script type="text/javascript" src="${path}/ext/locale/ext-lang-zh_CN.js"></script>
运行后 浏览器提示

Uncaught TypeError: Cannot read property 'model' of undefined localhost/:3
Uncaught TypeError: Cannot call method 'confirm' of undefined