How do I check if a browser supports HTML5 and CSS3 features using Ruby?

I need to make an if statement using Ruby that checks to see if the client's browser support HTML5开发者_高级运维 or not.

Short version: you won't be able to, nor should you.

Long version: It may be possible, if you do some user-agent sniffing, to identify whether or not the user's browser supports HTML5 or not. But this would take a fair amount of effort to get right. The better solution is to use something like Modernizr (http://www.modernizr.com/) to do your feature detection on the client-side.

It's possible to read the browser info based on the HTTP_USER_AGENT string, but, as mentioned above and many other places, it's also really easy to spoof that info. On the server-side we only cared because it gave us an overall view of the client browsers being used to access our sites.

Trying to react to a browser on the backend and present different content was tried by sites for a while, but it fails because of how browsers spoof other browsers, but don't have the same bugs.

As @Stephen Orr said, CSS is a better way of dealing with it. Sure it's hell and still error-prone, but it's better than sniffing the browser's signature. We used to cuss every release of IE because it broke the previous fixes. Luckily things seem to be getting better as the vendors creep toward toeing standards.

Most features can be detected (with JavaScript), but some kinds like the form-date-feature field is a problem: http://united-coders.com/matthias-reuter/user-agent-sniffing-is-back

It is possible to do Feature detection on HTML5, to detect single features from HTML5 as you need them. There is, however, no way to detect if a browser supports HTML5 as one big chunk - as there is no "official" way to tell if a browser supports all of HTML5 or just parts of it.

< [html5 element]  id="somethingtobedazzledby">
    Upgrade your browser
</ [html5 element] >