询问问题

jerrygu625 · 发表于 2016-8-12 11:36:05

问个问题
index.html
<!doctype html>
<html>
<head>
<title>版本</title>
<meta charset="utf8">
<script src="js/a.js"></script>
</head>
<body>
<script language="javascript">document.write(navigator.userAgent.toLowerCase());</script>
<script language="javascript">document.write(B);</script>
</body>
</html>

js/a.js
B=(function x(){})[-5]=='x'?'FF3'

function x(){})[-6]=='x'?'FF2':/a/[-1]=='a'?'FF':'\v'=='v'?'IE':/a/.__proto__=='//'?'Saf':/s/.test(/a/.toString)?'Chr':/^functiom \(/.test([].sort)?'Op':'Unknow'

open index.html with 2345explorer
mozilla/5.0 (windows nt 6.3; wow64) applewebkit/537.36 (khtml, like gecko) chrome/47.0.2526.108 safari/537.36 2345explorer/7.0.0.12291
Unknow

open index.html with Firefox
mozilla/5.0 (windows nt 6.3; wow64; rv:47.0) gecko/20100101 firefox/47.0
Unknow

为什么B总是为Unknow，网站说比navigator.userAgent更准确