为什么显示的是undefined
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>
<script type="text/javascript">
var b_code=Navigator.appCodeName;
var b_name=Navigator.appName;
var b_version=Navigator.appVersion;
var b_plat=Navigator.platform;
var b_user=Navigator.userAgent;
document.write(b_code+"<br/>");
document.write(b_name+"<br/>");
document.write(b_version+"<br/>");
document.write(b_plat+"<br/>");
document.write(b_user+"<br/>");
</script>
<body>
</body>
</html>
