POST variable from jquery redirecting but is not set

I asked a question recently about sending a POST variable off of jquery to another php page, redirecting to that page, doing some action with the sent information, and redirecting off of the original page.

jQuery post method and directory confusion

I am asking for help on almost the exact same code, since the person who commented on it only answered half of my question and marked it as a duplicate. While it did help, it did not solve the problem.

I have made edits according what was suggested in the previous attempt to get this problem solved. As you will see, hitting the save button in this example will bring you to changePage.inc.php, the first redirect, but the second redirect does not happen, which should bring you to secondPage.php.

File named index.php

<?php
    session_start();
?>

<!DOCTYPE html>
<html>
<script src="https://code.jquery.com/jquery-3.2.1.min.js"
    integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4="
    crossorigin="anonymous">
</script>
<script>
    $(document).ready(function(){
        $('#saveForm').submit(function(event){
            event.preventDefault();
            var message = "";

            var changeText = function(){
                message = "You wrote: " + $('#text').val();
            };

            var send = function(){
                if(message !== ""){
                    $.post("includes/changePage.inc.php", {message: message});
                    window.location.href = "includes/changePage.inc.php";
                }
            };

            changeText();
            send();
        });
    });
</script>
<body>
<textArea id="text"></textArea>
<form id="saveForm" action="includes/saveEssay.inc.php" method="POST">
  <button type="submit" id="saveButton">Save!</button>    
</form>
</body>
</html>

File named changePage.inc.php (within a folder named includes)

<?php

session_start();

if(isset($_POST['message'])){
    header("Location: ../secondPage.php");
}

exit();

File named secondPage.php

<?php
    echo 'Hello World';
?>

The jQuery $.post() method is what is referred to as an asynchronous call. What this means is that while $.post() is trying to execute, any line of code after it will try to execute.

Note that you're redirecting immediately after your $.post(). This means that while $.post() is trying to run, you're redirecting to includes/changePage.inc.php, which is probably preventing the PHP redirect to ../secondPage.php from running. This is what we call a race condition, where two events are running simultaneously and either one could finish before the other with no way to keep the events synchronized.

What you're really trying to do, from what I can tell, is hand off processing of your data to PHP, then upon finishing, you want to redirect to a given page.

If I'm correct about this, then remove the window.location.href = "includes/changePage.inc.php"; line because otherwise you're always going to run into issues with this race condition. Handle the redirect in PHP--it should work on its own. If you're having trouble with redirecting directly in PHP, then you can redirect through jQuery:

Your jQuery POST

$.post("includes/changePage.inc.php", {message: message}, function(data) {
    var obj = $.parseJSON(data);
    window.location.href = obj.redirect_url;
});

What to return via PHP

echo json_encode(array('redirect_url'=>'includes/secondPage.php'));

If this doesn't meet your needs, then you'll need to really sit down and better explain your use case and your intent. If you can't explain it well enough to communicate exactly what you want, then you probably don't have a complete grasp of the problem you need to solve.

来源：https://stackoverflow.com/questions/46778066/post-variable-from-jquery-redirecting-but-is-not-set

标签

php

jquery

redirect

post

isset