Ext 2.3 树 treeloader 无法加载

直接上代码，
以下是html<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>简单树</title>
<link rel="stylesheet" type="text/css" href="jslib/ext-2.3.0/resources/css/ext-all.css">
  <script type="text/javascript" src="jslib/ext-2.3.0/adapter/ext/ext-base.js"></script>
  <script type="text/javascript" src="jslib/ext-2.3.0/ext-all.js"></script>
  <script type="text/javascript">
  Ext.onReady(function(){     var root = new Ext.tree.AsyncTreeNode(
         {
         text:'根',
         loader: new Ext.tree.TreeLoader({dataUrl: 'data.js'})
         }
         );
    var tree = new Ext.tree.TreePanel({
        el: 'tree',
        root:root
    });     
    tree.render();
});
  </script>
</head>
<body>
   <div id='tree'  style="width:500px;height:400px;border:1px solid #000000"></div>
</body>
</html>
data.js
[{
        id: 1,
        text: '子节点1',
        leaf: true
    },{
        id: 2,
        text: '儿子节点2',
        children: [{
            id: 3,
            text: '孙子节点',
            leaf: true
        }]
   }]运行时无法加载孩子节点