[Javascript] Javascript detection

[Paul Novitski]

At 1/2/2007 11:35 AM, tedd wrote:
>Now, how to get around not downloading a test page before presenting 
>the "final" product I don't think is possible for one has to use js 
>to see if it's there, or not, before passing that condition back to 
>the server, right?
>
>If you have a different method, I would love to hear it.


Hi Tedd,

There's such a discontinuity between the server and the client that I 
think the best you can hope for is a probability, not a surety, that 
a particular condition exists on the client side.  You can make 
assumptions when you download a page to the client that might cease 
to be true by the time the page renders or at any time during the 
user's interaction with the page, and you can make assumptions on the 
basis of what you get back from the client that might no longer be 
true by the time you download the next page.

I think the problem you're ultimately trying to solve is faux.  The 
server CAN'T know whether or not javascript "is running" because the 
server-side script completes its execution before the page finishes 
rendering and the user interacts with it client-side.  It's like 
deciding whether to leave your great-great-grandchild an inheritance 
of a comb based on whether they've got long hair.  The expression of 
the problem infers a simultaneity that just isn't there.  Even if you 
could look ahead in time and see that the child has hair and how long 
it is, by the time that child is born and reaches the age of 
inheritance they may have decide to cut their hair or they might be 
undergoing medication that causes them to lose it entirely.  Better 
to leave an inheritance that they can use regardless.

So I believe a more robust approach to web design is to deliver pages 
that work whether or not javascript is running.  If the user can 
interact with the page controls as enhanced by javascript, then 
disable javascript, then continue interacting with the page 
successfully, I would slap that page with a big fat gold star.  In 
that model the server doesn't attempt to determine whether or not 
javascript is running, it downloads pages that can accommodate both scenarios.


Back to your problem, though:  For reasons I don't know you've 
rejected suggestions of using POST and GET and cookies which are the 
primary mechanisms we've been given to share information between 
client & server.  I wouldn't want to discourage you from cutting a 
new path -- go for it, maybe you'll figure out something that no one 
else has seen -- but I would think it would be somewhat more 
efficient to find a means that does use the familiar methods.

For example, here's one using GET:

         <a 
href="switchboard.php?something=123456&dest=contact.php">Contact Us</a>

That is, pass a value to PHP which it can store any way you want 
between page-views, then redirect to the desired page.  This link 
will work whether or not javascript is running, although if js is 
enabled it could modify the querystring to enhance the process.

Here's one using POST:

         <form action="contact.php">
                 <input type="hidden" value="123456" name="something" />
                 <input type="submit" value="Contact Us" />
         </form>
or:
         <form action="switchboard.php">
                 <input type="hidden" name="something" value="123456" />
                 <input type="hidden" name="destination" value="contact.php" />
                 <input type="submit" value="Contact Us" />
         </form>

Here again, javascript can create, modify, and delete hidden form 
fields at any time until submit, and can take control of the submit 
method to work its magic at the last instant.

As long as you're using a double hit on the server to accomplish your 
goal, I would imagine these solutions could fit inside your 
parameters (as I guess them to be).

Regards,
Paul