PHP file not picking up $POST parameter from JQuery - php

Question

Thank you very much for your help. I have the following file. The two alerts in the jquery event listener both work, but not the one inside the if (isset) block, as it is posting to itself. Thank you very much! I have abbreviated the code, everything is inside its proper tag.
<?php session_start();
include("config.php");
$myID = $_POST['chatid'];
$_SESSION['chateeID'] = $myID;
if(isset($_POST['inputmessage'])) {
echo '<script type="text/javascript">alert("got in here");</script>';
$sMessage = mysqli_real_escape_string($_POST['inputmessage']);
if ($sMessage != '') {
$sql = "INSERT INTO chatmessages (user_one_id, user_two_id, mymessage, action_user_id)
VALUES ('$user1', '$user2', '$sMessage', '$action_user_id')";
// Perform a query, check for error
if (!mysqli_query($con,$sql)){
echo '<script type="text/javascript">alert("'.mysqli_error($con).'");</script>';
}
}
}
<script>
$('#ChatInputBox').keydown(function (e) {
var keyCode = e.keyCode || e.which;
var txt = $("#ChatInputBox").val();
if (keyCode == 13 && txt!="") {
alert("txt is: "+txt);
$.post("inserttochat.php", { inputmessage: txt }, function(result){
alert("got to callback!");
});
}
});
</script>
I did this exactly the same way on another page but cannot find the discrepancy here.

Answer 1

After setting up your code on my development system I discovered that the short piece of script your PHP code is sending is being sent correctly, and being received correctly but not being executed by the jQuery AJAX code.
If you want that alert to show up in your page you need to place it in an HTML element
<div id="response"></div>
then
$.post("inserttochat.php", { inputmessage: txt }, function(result){
alert("got to callback!");
$("response").html(result);
});
A better way to do this is to echo some sort of status as a JSON object, then unpack that into an alert in Javascript.
echo json_encode((object)['status'=>'ok', 'msg'=>'All good']);
then
$.post("inserttochat.php", { inputmessage: txt }, function(result){
alert("Response: "+result.status+', '+result.msg);
},'json');
Note the json datatype added to the POST request*.
A better approach here is to standardise all your responses as JSON, and then add header("Content-type: application/json"); at the top of your PHP files. This will tell jQuery what the data is, rather than you having to force the issue in the browser.