Access a Javascript variable from PHP

Question

I need to access a javascript variable with php. Here's a stripped-down version of the code I'm currently trying, which isn't working:

 <script type="text/javascript" charset="utf-8">
   var test = "tester";
 </script>

 <?php
 echo $_GET['test'];
?>

I'm a complete noob at both js and php, so would really appreciate any advice.

UPDATE: OK, I guess I simplified that too much. What I'm trying to do is create a form that will update a twitter status when submitted. I've got the form working OK, but I want to also add geolocation data. Since I'm using Javascript (specifically, the Google Geolocation API) to get the location, I need to somehow access that info with php when I'm submitting the form.

Answer 1

_GET accesses query string variables, test is not a querystring variable (PHP does not process the JS in any way). You need to rethink. You could make a php variable $test, and do something like:

<?php
$test = "tester";
?>
<script type="text/javascript" charset="utf-8">
    var test = "<?php echo $test?>";
</script>

<?php
    echo $test;
?>

Of course, I don't know why you want this, so I'm not sure the best solution.

EDIT: As others have noted, if the JavaScript variable is really generated on the client, you will need AJAX or a form to send it to the server.

Answer 2

JS ist browser-based, PHP is server-based. You have to generate some browser-based request/signal to get the data from the JS into the PHP. Take a look into Ajax.

Answer 3

The short answer is you can't.

I don't know any PHP syntax, but what I can tell you is that PHP is executed on the server and JavaScript is executed on the client (on the browser).

You're doing a $_GET, which is used to retrieve form values:

The built-in $_GET function is used to collect values in a form with method="get".

In other words, if on your page you had:

<form method="get" action="blah.php">
    <input name="test"></input>
</form>

Your $_GET call would retrieve the value in that input field.

So how to retrieve a value from JavaScript?

Well, you could stick the javascript value in a hidden form field...

<script type="text/javascript" charset="utf-8">
    var test = "tester";
    // find the 'test' input element and set its value to the above variable
    document.getElementByID("test").value = test;
</script>

... elsewhere on your page ...

<form method="get" action="blah.php">
    <input id="test" name="test" visibility="hidden"></input>
    <input type="submit" value="Click me!"></input>
</form>

Then, when the user clicks your submit button, he/she will be issuing a "GET" request to blah.php, sending along the value in 'test'.

Answer 4

As JavaScript is a client-side language and PHP is a server-side language you would need to physically push the variable to the PHP script, by either including the variable on the page load of the PHP script (script.php?var=test), which really has nothing to do with JavaScript, or by passing the variable to the PHP via an AJAX/AHAH call each time the variable is changed.

If you did want to go down the second path, you'd be looking at XMLHttpRequest, or my preference, jQuerys Ajax calls: http://docs.jquery.com/Ajax

Answer 5

If showing data to the user, do a redirect:

<script language="JavaScript">
    var tester = "foobar";
    document.location="http://www.host.org/myphp.php?test=" + tester;
</script>

or an iframe:

<script language="JavaScript">
    var tester = "foobar";
    document.write("<iframe src=\"http://www.host.org/myphp.php?test=" + tester + "\"></iframe>");
</script>

If you don't need user output, create an iframe with width=0 and height=0.