What is the market penetration like for JavaScript? I know of many articles (all a few years old) that have investigated how big a percentage has JavaScript disabled.
I am developing a very JavaScript-heavy site now, and would very much like to know how large a percentage of the world browse without JavaScript enabled.
I don't think that many people just turn javascript off anymore. However, things like NoScript --where javascript is disabled for a site initially and must be explicitly enabled-- are becoming more popular.
Additionally there are a few classes of browser that won't run your javascript as intended:
Go ahead and use javascript. But make sure the site will fall back to something decent if the javascript doesn't work as expected.
Finally, I'll edit in a point someone else brought up below. If you do work for the government you may be required to support the first class of browser I listed above.
On average you should count 5% of users without javascript, but I guess that figure can change depending on your target audience.
Most of the JS Off crowd, I think, is made up of corporate guys that have it disabled by they sysadmins and very restrictive IE settings; the other part being extreme geeks that hate "fancy/new" technologies - which doesn't really apply to javascript when it's done right, but just like flash it has been misused a lot.
According to http://visualrevenue.com/blog/2007/08/eu-and-us-javascript-disabled-index.html, data collected in 2007, 1.04% have it disabled in the EU, and 3.05% have it disabled in the US.
The problem is more apparent on mobile browsers, but you will likely serve different content to them anyway,
Many normal users have JavaScript enabled, but what's your target audience? If you work in the government, health care (or similar) sectors, you may want to be a little more careful about how you handle users that don't have scripting enabled.
w3C stats are rubbish, mostly devs visit the site so can be taken with a pinch of salt really. I would say if you discount mobile, console clients then you would arrive at around 1-2% of your user base. If you have an e-commerce site then 1% could be a significant sum but is it worth the extra effort to develop non-js content, also should you dent the user experience of 99% of your users to cater for 1%? It depends, maybe your app has to be fully compliant (government etc).
I use NoScript with FireFox to selectively disable features like scripting. I started out using FireFox because of the tabs, but I stay using it because of the fine-grained control I can get with plugins like NoScript.
So if your site was worth it to me, I could enable script for it. But that's a fine balance and my default position is script off.
I would design based on the default configuration of the vanilla install of all major browsers and test to make sure it degrades nicely. If you take time to factor all of the tweaks individual users can do via add-ons like NoScript and extreme security settings you'll never end up shipping.
Well, think about it for a second, how many general public even knows what javascript is, let alone disable it? For these of us who do know, only a very small percentage completely disables it. So I don't think you really should worry too much about this.
While there are certainly very few people that browse with Javascript disabled, your site should still function without it. If you're creating a design already knowing for a fact that a group of people won't be able to use it, even if that group is extremely small, it's not a good design.
As Joel Coehoorn pointed out, if you develop only for desktops, you can assume JavaScript will be turned on, with the only relevant exception of Screen readers/accessible browsers (which may be an issue when working for governments and large enterprises).
On the other hand, you may want to design a special version of your website/application for mobile devices, which are rapidly increasing their market share. But in that case, JavaScript is not your only concern. You should really develop all your Web UI for a smaller media. FaceBook Mobile is a nice example.
Now that browsers let you block Javascript from certain operations (pop-ups, moving the window, overriding right-click menus) there's fewer reasons to disable it altogether.
Try not to rely on the features that are commonly disabled though. Firefox disables a few by default.
At this very moment I'm working behind a firewall that blocks some Javascript, as part of the corporate protection against malware. I would probably show up in the stats as Javascript enabled, but the user experience is poor. For example, clicking on the "comments" links on this page will not show the comments for me. This is absolutely out of my control.
I'm sure this is not the only corporate environment which works this way.
I use NoScript at home, but usually turn it off when shopping, as it tends to break cross server payment authorisations etc. Although this is only the case for sites I've not used before, it's still a bit of a pain.
The percentage of users without it is irrelevant, the question is do you want to support those users? The answer should almost always be yes (there are instances when its ok to be no), but when it comes to the level of support thats when your individual requirements come in. The usual thing is to give people with JS enabled extra in-page features than those without, for instance hiding content that shows on demand or using Ajax to avoid post-backs.
To cite adactio: "Is an acceptable proportion of your target market likely to have JavaScript enabled, or is your service so useful that people will go out of their way to acquire JavaScript capabilities to use it?"
My Logic:
NoScript users, console users and web hackers and such ARE advanced users. They have JavaScript disabled because they CAN enable it if they want. They don't need no-JavaScript support.
The poor corporate sods behind no-JavaScript firewalls (and square wheels, no hot water) are few but might be important for your site. They and the disabled do need some level of progressive enhancement.
Then there are mobiles (of which, nowadays majority do have JavaScript support as well), which need different type of site.
and lastly the bots. They don't need SEO optimized site.
But the best way all this can be achieved is alternate content. If it is detected that JavaScript is disabled, then offer a low-resolution (mobile) version of the site.