How to detect if JavaScript is disabled?

Question

There was a post this morning asking about how many people disable JavaScript. Then I began to wonder what techniques might be used to determine if the user has it disabled.

Answer 1

I'd like to add my .02 here. It's not 100% bulletproof, but I think it's good enough.

The problem, for me, with the preferred example of putting up some sort of "this site doesn't work so well without Javascript" message is that you then need to make sure that your site works okay without Javascript. And once you've started down that road, then you start realizing that the site should be bulletproof with JS turned off, and that's a whole big chunk of additional work.

So, what you really want is a "redirection" to a page that says "turn on JS, silly". But, of course, you can't reliably do meta redirections. So, here's the suggestion:

<noscript>
    <style type="text/css">
        .pagecontainer {display:none;}
    </style>
    <div class="noscriptmsg">
    You don't have javascript enabled.  Good luck with that.
    </div>
</noscript>

...where all of the content in your site is wrapped with a div of class "pagecontainer". The CSS inside the noscript tag will then hide all of your page content, and instead display whatever "no JS" message you want to show. This is actually what Gmail appears to do...and if it's good enough for Google, it's good enough for my little site.

Answer 2

Why don't you just put a hijacked onClick() event handler that will fire only when JS is enabled, and use this to append a parameter (js=true) to the clicked/selected URL (you could also detect a drop down list and change the value- of add a hidden form field). So now when the server sees this parameter (js=true) it knows that JS is enabled and then do your fancy logic server-side.
The down side to this is that the first time a users comes to your site, bookmark, URL, search engine generated URL- you will need to detect that this is a new user so don't look for the NVP appended into the URL, and the server would have to wait for the next click to determine the user is JS enabled/disabled. Also, another downside is that the URL will end up on the browser URL and if this user then bookmarks this URL it will have the js=true NVP, even if the user does not have JS enabled, though on the next click the server would be wise to knowing whether the user still had JS enabled or not. Sigh.. this is fun...

Answer 3

I assume that you're trying to decide whether or not to deliver JavaScript-enhanced content. The best implementations degrade cleanly, so that the site still operates without JavaScript. I also assume that you mean server-side detection, rather than using the <noscript> element for an unexplained reason.

There is not a good way to perform server-side JavaScript detection. As an alternative it is possible to set a cookie using JavaScript, and then test for that cookie using server-side scripting upon subsequent page views. However this would not be suitable for deciding what content to deliver as it would not be able to distinguish visitors without the cookie from new visitors or visitors who are blocking cookies.

Answer 4

Because I always want to give the browser something worthwhile to look at I often use this trick:

First, any portion of a page that needs JavaScript to run properly (including passive HTML elements that get modified through getElementById calls etc.) are designed to be usable as-is with the assumption that there ISN'T javaScript available. (designed as if it wasn't there)

Any elements that would require JavaScript, I place inside a tag something like:

<span name="jsOnly" style="display: none;"></span>

Then at the beginning of my document, I use .onload or document.ready within a loop of getElementsByName('jsOnly') to set the .style.display = ""; turning the JS dependent elements back on. That way, non-JS browsers don't ever have to see the JS dependent portions of the site, and if they have it, it appears immediately when it's ready.

Once you are used to this method, it's fairly easy to hybridize your code to handle both situations, although I am only now experimenting with the noscript tag and expect it will have some additional advantages.

Answer 5

You might, for instance, use something like document.location = 'java_page.html' to redirect the browser to a new, script-laden page. Failure to redirect implies that JavaScript is unavailable, in which case you can either resort to CGI ro utines or insert appropriate code between the tags. (NOTE: NOSCRIPT is only available in Netscape Navigator 3.0 and up.)

credit http://www.intranetjournal.com/faqs/jsfaq/how12.html

Answer 6

noscript blocks are executed when JavaScript is disabled, and are typically used to display alternative content to that you've generated in JavaScript, e.g.

<script type="javascript">
    ... construction of ajaxy-link,  setting of "js-enabled" cookie flag, etc..
</script>
<noscript>
    <a href="next_page.php?nojs=1">Next Page</a>
</noscript>

Users without js will get the next_page link - you can add parameters here so that you know on the next page whether they've come via a JS/non-JS link, or attempt to set a cookie via JS, the absence of which implies JS is disabled. Both of these examples are fairly trivial and open to manipulation, but you get the idea.

If you want a purely statistical idea of how many of your users have javascript disabled, you could do something like:

<noscript>
    <img src="no_js.gif" alt="Javascript not enabled" />
</noscript>

then check your access logs to see how many times this image has been hit. A slightly crude solution, but it'll give you a good idea percentage-wise for your user base.

The above approach (image tracking) won't work well for text-only browsers or those that don't support js at all, so if your userbase swings primarily towards that area, this mightn't be the best approach.