火狐，谷歌，IE，全都是undefined
<script type="text/javascript">
document.write(Navigator.appCodeName+"<br>");
document.write(Navigator.appName+"<br>");
document.write(Navigator.appVersion+"<br>");
document.write(Navigator.platform+"<br>");
document.write(Navigator.userAgent+"<br>");
</script>
火狐，谷歌，IE，全都是undefined
