问题
We know it's possible to look up the IP of a visitor using JSON and a callback, as seen here Can I perform a DNS lookup (hostname to IP address) using client-side Javascript? and also at http://news.ycombinator.com/item?id=1896015 - but what about a similar thing for the user agent?
回答1:
This string is directly available in navigator.userAgent. However, this string is not very reliable, because the user can easily modify it. Only use it for non-critical purposes.
If you want to detect the user agent, so that you "know" what's supported, you'd better switch to capability-detection.
Examples of alternative methods to detect the browser:
- IE: Conditional comments (HTML (also includes IE version) or in JScript)
- Firefox / Webkit / Opera: Setting a CSS property with a vendor-prefix, and checking for the existence of the just-set property.
回答2:
navigator.userAgent contains the user agent string of the browser.
来源：https://stackoverflow.com/questions/9009774/can-i-look-up-the-user-agent-from-javascript