AJAX / PHP error handling and global variable - php

Question

this is my first time writing an ajax below is my structure
submitted.php
<?php $a = $_POST['a']; // an input submitted from index.php ?>
<button>bind to jquery ajax</button> // call ajax
<span></span> // return ajax result here
<script>
$('button').on('click', function() {
event.preventDefault();
$.ajax({
method: "POST",
url: "test.php",
data: { "key" : 'data'}
})
.done(function( msg ) {
$('span').html(msg);
});
});
</script>
test.php
<?php echo $a; // will this work? ?>
ajax return blank... no error, my error_reporting is on.

Answer 1

No, there are a few things wrong with this:
You are posting a key - value pair where the key is key, so you would need $_POST['key'] in your php script;
You should use .preventDefault() if you need to prevent an event like a form submit that is caused by your button. If that is the case, you need to get the event variable from your event handler: $('button').on('click', function(event) {.If there is no event to prevent, you can simply remove that line;
If you do have a form (it seems so from your comment), you can easily send all key - value pairs using: data: $('form').serialize().

Answer 2

form.php
<button>bind to jquery ajax</button> <!-- ajax trigger -->
<span></span> <!-- return ajax result here -->
<script>
// NOTE: added event into function argument
$('button').on('click', function(event) {
event.preventDefault();
$.ajax({
method: "POST",
url: "test.php",
data: { "key" : 'data'}
})
.done(function(msg) {
$('span').html(msg);
});
});
</script>
process.php
<?php
echo (isset($_POST['key'])) ? $_POST['key'] : 'No data provided.';
?>

Answer 3

This is the way to do it:
ubmitted.php
<button>bind to jquery ajax</button> // call ajax
<span></span> // return ajax result here
<script>
$('button').on('click', function() {
// no need to prevent default here (there's no default)
$.ajax({
method: "POST",
url: "test.php",
data: { "key" : 'data'}
})
.done(function( msg ) {
$('span').html(msg);
});
});
</script>
test.php
<?php
if (isset($_POST['key'])
echo $_POST['key'];
else echo 'no data was sent.';
?>