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I know there have been tons of questions about setting a PHP session from JQuery and then returning it to JQuery. And I have looked at all of them and still cannot figure out why my code doesn't work. I am trying to use a modal to set a PHP session variable on a back end PHP page and then display it in another modal using jquery, but nothing gets returned.

Here is my sending modal:

<div id="sendingModal" class="modal" tabindex="-1" role="dialog">
 <div class="modal-dialog modal-md" role="document">
  <div class="modal-content">
   <div class="modal-body">
    <button id="testSession" type="button" class="btn btn-secondary">Session Test</button>
   </div>
  </div>
</div>

and here is my back end php:

<?php
  session_start();
  $_SESSION['testInput'] = $_POST['inputData'];
?>

and here is my receiving modal:

<div id="receivingModal" class="modal" tabindex="-1" role="dialog">
 <div class="modal-dialog modal-md" role="document">
  <div class="modal-content">
   <div class="modal-body">
    <div id="testDiv"></div>
   </div>
  </div>
</div>

Here is my JQuery:

$(document).ready(function() {
 $('#testSession').on('click',function(e){
   var testData = 'testing 123';
   $.post("backendSession.php", {"inputData": testData});
   $('#testSession').html(<?=$_SESSION['testInput']?>);
   $('#testModal').modal('show');
 });
});

What am I doing wrong?

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  • 2
    I believe you've hit the confusion distinction between server-side code and client-side code. Once PHP is done, the generated html is sent to the client. Then the client runs javascript. In order to get more data back, you send a new request (either in ajax, or direct). You must then handle the return data from that new request... which is where you are not in your .post call. Commented Jul 27, 2018 at 15:54
  • So the data flow you need to be following is something like: PHP creates HTML content that is displayed to the user. User clicks something which triggers an event that sends data to your backend script via AJAX. This backend script creates the session variable you need AND THEN returns this value to the same script that made the AJAX call. When that happens you'll have the session value ready at your disposal. Commented Jul 27, 2018 at 16:02
  • The php isn't sending html back to the client. It's setting a server-side session variable. the .post is what calls the php to do that. I'm handling the data when I set the html of the #testSession div to the session variable. Is that not right? Commented Jul 27, 2018 at 16:03
  • 1
    You don't have to return HTML.. you can return a JSON encoded array of values. Take a look at $.ajax(). There's a success callback which handles all the returned data after calling the backend script. Commented Jul 27, 2018 at 16:06
  • 1
    @IncredibleHat yes I believe $.post() and $.get() both call $.ajax() with pre-defined settings. I just prefer using $.ajax() - not saying OP can't use the others. Commented Jul 27, 2018 at 16:10

1 Answer 1

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You only have a small issue here, and its a simple fix based on the code you provided. You MUST return the new data back during the ajax call, or you will not be able to use it (not until, that is, a whole new page refresh).

First up, add to your backendSession.php:

<?php
    session_start();
    $_SESSION['testInput'] = $_POST['inputData'];
    echo htmlspecialchars( $_SESSION['testInput'] );// new bit
?>

Then adjust your .post usage as follows:

$(document).ready(function() {
    $('#testSession').on('click',function(e){
       var testData = 'testing 123';
       $.post("backendSession.php",
              {"inputData": testData},
              function( rawdata ) {                  // add return handler callback
                  $('#testDiv').html( rawdata );     // use the return data
                  $('#testModal').modal('show');     // show the modal
              }
       );
    });
});

Now that is the basic change to make what you were wanting to do. However you may want to deal with JSON return data in the future, if you plan on needing more than just an echo of the input. An example of that will go beyond the question though ;)

As another side: You probably will want to sanitize that post input. I know what you provided was a minimal example, but I just wanted to mention it. As simply echoing out the raw user input, back into a page, can open up some XSS attack vectors.

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4 Comments

I still get nothing in the receiving modal
I used the code you were using. Maybe you didn't actually mean $('#testSession').html to be set? But rather $('#testDiv').html?
It was supposed to be #testDiv. Duh. Thanks, Hat.
Ok, I adjusted the answer to reflect that :)

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