Passing javascript variable to PHP

I have a question:

Since Javascript is client-side and PHP is a server-side, and HTTP is a "stateless" protocol, therefore the two languages cannot directly share variables. Would it be possible to pass a variable from Javascript to PHP?

You could try loading it via an Image object (untested, I'm no JS guru):

<script>
bar = 'something';

img = new Image();
img.src ='/file.php?foo=' + encodeURIComponent( bar );
delete img;
</script>

...or if you have some AJAX magic happening, sneak it through as an additional parameter.

It's not possible, directly. You can use AJAX to make them 'interface', but that's about it. AJAX will send a request to a file using either GET or POST, which you'll be familiar with in PHP. So, if you had a script to handle the ajax sent information, you'll be able to interface with the JS based on the return from the PHP script.
Indirectly, you can set up a JS redirect with the information in the URL (via GET), which you can pick up in PHP ($_GET). It does mean you'll leave the current page the JS executed on, and move on to the processing script (maybe that's what you're looking for anyway).

In a very loose sense, you can 'pass' a PHP variable into JS without AJAX. I say very loose, because you're not actually talking to the JS in real time - you output the actual JS with PHP, echoing the relevant parts. You're generating the JS code to run, as opposed to actually running the two in real time and 'passing' a variable.

@kbluhm, I don't think the image would work. As the output from the PHP script would have to be an image content-type (I'm pretty sure) for the JS to interact with it. For your method, it would be much easier to just set up a JS redirect like I said above, or AJAX like you touched on. No need to try and sneak it in an image.

@kbluhm, I don't think the image would work. As the output from the PHP script would have to be an image content-type (I'm pretty sure) for the JS to interact with it. For your method, it would be much easier to just set up a JS redirect like I said above, or AJAX like you touched on. No need to try and sneak it in an image.

I'm pretty sure an image-related content type makes no difference, since you can deliver an image with a content type of application/octet-stream, etc. All you're doing is creating a HTTP request, I doubt client-side JavaScript gives a rats rump about the server-side content type. :)

So since you brought it up, this is now tested and confirmed. It worked in all browsers I cared to test it in: IE, FF, Chrome, Safari, and Opera. :thumbsup:

index.html

<script>
bar = 'something';

img = new Image();
img.src ='./file.php?foo=' + encodeURIComponent( bar );
delete img;
</script>


file.php

<?php

file_put_contents( './data.txt', $_GET['foo'] );


data.txt, after viewing index.html
something

Haha I'll reword :P. My main, admittedly ambiguous, point was that your method would render the value useless unless you were writing it to a file, or assigning the value to a database or something similar. It would provide no return (to my knowledge) whereas a redirect would take you to the script itself, or an AJAX request would provide a return based on the input (potentially the best option).

Depends on what the OP wants.

Once again you're not re-wording; you're changing. You said the image wouldn't work... then after seeing it does you said let me reword. Am I confused or are you? :)

What I mainly meant is that it doesn't offer any return. Your image will pass a value into the PHP to do whatever, but it doesn't give an opportunity for return values. Whereas AJAX would, and a redirect would run the script (obviously) through navigation.

However the whole meaning to what I said, was that I thought JS would give an error relating to the image-type. Would this not cause problems with other parts of javascript?

I didn't change the meaning to my reply.