Require Javascript on site?

[RichardGv]

This is how I consider the whole thing:

1. If there's something that can be achieved with either JavaScript or HTML/CSS, I would prefer CSS. There are some people, like me, who tend to disable JavaScript due to security consideration. But there are very few ones disabling CSS. for CSS almost never brings any secuirty issues. (It's indicated that @font-face may brings security problems, though.) Also, a static CSS could be more efficient than JavaScript during execution, I think. (This point is unproved.)
   
2. If there's something that can only be achieved with JavaScript, it's needed to use it. But a graceful downgrade when JS is not enabled, and a friendly notification, are preferred.
   
3. Between Flash and HTML5, I would prefer HTML5. Flash has a long history of security flaws and potentially more dangerous than JavaScript and other features built-in in browsers, with more access to other parts of the system. Not to mention it's lack of a proper 64-bit version (It used to have one, but Flash 10.1 comes with no x64 version).
   
4. I don't think there's a point to require JavaScript in a "casual" website, unless you have very specific needs, for instance, video playback, complicated presentation, instant messaging or chat, in-browser games. Several types of most commonly used scripts, i.e. blogs, CMS, forum systems, usually use JavaScript (and these JavaScript does improve productivity, e.g. Ajax features), but don't explicitly require JavaScript (i.e. downgrading gracefully when JavaScript is disabled), and that's the approach I prefer. Another possiblity is to redirect users disabling JavaScript to a special "?noscript=1" page, which is used by several big sites as well.
   
5. Still, most people don't keep JavaScript disabled. I believe more than 98% of visitors here have JavaScript enabled. So, requiring JavaScript or not don't make a significant difference, as far as the JavaScript code is properly written and don't cause serious performance issues.
   

And my personal opinion here, which, I guess, is largely different from most of your visitors: From the perspective of a user, I dislike sites that use unnecessary JavaScript. Following a very paranoid policy, I heavily relies on NoScript, and forbids JavaScript, Flash, Java, Meta redirection, web bugs, audio, video, @font-face. bookmarklets, XSLT, iframe, frames, and cookies on any website that I've not explicitly marked as trusted. If a site that I don't trust relies on JavaScript, I will generally refuse viewing the site. You can consider developing a JavaScript-less website if you think your visitors have such paranoia thought process. :)

Note: I'm not an expert in web development, especially the frontend. My statements above can be wrong.