The basic question: When specifically are the $_POST and $_GET variables set? The reason I ask is explained below.
Advance disclosure: The file I am sharing here is for testing/learning purposes, and doesn't aim to achieve anything useful. I wrote it in order to isolate this one question from the other details of the project I am working on.
Here's a summary of what I'm trying to do: I call a javascript function from a form
<form action="javascript:jsTest()" ... />
and then from within jsTest() I assign a javascript variable based on the return of a php function, phpTest():
var jsVar = <?php echo json_encode(phpTest()); ?>;
The function phpTest() simply returns a $_POST variable:
return $_POST['testName'];
Here's the full code:
<?php
session_start();
function phpTest() {
return $_POST['testName'];
}
?>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>javascript/php test</title>
<script type="text/javascript">
function jsTest() {
var jsVar = <?php echo json_encode(phpTest()); ?>;
alert(jsVar);
}
</script>
</head>
<body>
<form method="POST" name="testForm" action="javascript:jsTest()">
<input type="text" name="testName" value="username" />
<input type="submit" value="submit" />
</form>
</body>
</html>
The problem: alert always displays null.
I tested this in two ways. 1) If instead I set the form action to a separate .php file, the $_POST variables associated with the form input fields are set, and an echo in that file, of those $_POST values, is shown in the browser. And alternatively, 2) if instead I return from phpTest() a simple string,
return 'hello kitty';
then the javascript alert() shows exactly that returned string. Therefore I believe it is safe to assume that the $_POST variable has not yet been set. Which brings me to the question I have not been able to find an answer to:
When exactly are $_POST variables set? I assumed it was before page reload (which my approach requires), and I assumed this because if I alternatively use method="GET" in my code, I see the GET variables tacked onto the URL without any prior page reload.
Thanks in advance.
Chris
As Marc B said with your current code example it will never work as you intend it to.
$_POST will always be availabe through out your script because it's one of PHP's superglobal arrays, however it may not have a value. $_POST has a value when POSTDATA is sent via a HTTP POST request. You can set the value of $_POST programaticly but that isn't cool. Ever.
For your script to work(ish) you need to send a HTTP POST request populated with some POSTDATA. You can do this using cURL or Firefox's Poster plugin.
POST /index.php HTTP/1.1
User-Agent: curl/7.21.4 (universal-apple-darwin11.0)
Host: example.org
Accept: */*
Content-Length: 16
Content-Type: application/x-www-form-urlencoded
testName=yeahboi
if you can view your HTTP response body the JavaScript variable JsVar should now be populated with 'yeahboi'.
Ive updated your script a little to submit the form via HTTP POST to it's self and populate a JavaScript variable.
<?php
// Script name: index.php
// Define a default value...
$name = 'unknown';
// Make sure post item 'testName' is available...
if(isset($_POST['testName']) &&
!empty($_POST['testName'])) {
// POST is available update name...
$name = $_POST['testName'];
}
?>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>javascript/php test</title>
<script>
// wait for the DOM to be ready then update the JS variable with PHP's $name variable
document.addEventListener('DOMContentLoaded', function() {
var elm = document.getElementById('post-response'),
value = '<?php echo $name; ?>';
elm.innerHTML = value;
}, false);
</script>
</head>
<body>
<div id="post-response"></div>
<form method="POST" name="testForm" action="index.php">
<input type="text" name="testName" value="username" />
<input type="submit" value="submit" />
</form>
</body>
</html>
Hope this helps you out a bit.