AJAX调用后会收到旧会话数据的警报

Question

I have an AJAX call that updates a $_SESSION variable, after that the <script> should echo out the new variable. The data is reaching the .php page, and also is being stored into the session. But it's alerting the old data after the AJAX call.
I've tried using setTimeout and also tried moving the call that alerts the new variable outside of the AJAX success call. I still get the same result.

Why isn't it alerting the new $_SESSION data?

AJAX

<script>
$(function() {
    $('#sendBtn').click(function() {                
        var theva = $("#element_23").val();                                 
         $.ajax({
         type   : "POST",
         url    :'check.php',
         data   : {theva : theva},
         success: function() {
             setTimeout(function() {
             var theva2 = "<? echo $_SESSION['disp'];?>";
             alert(theva2);},3000);}                        
         });                                
    });     
});
</script>

check.php

<? 
if($_POST){
$_SESSION['disp'] = $_POST['theva'];}
?>  

Answer 1

var theva2 = "<? echo $_SESSION['disp'];?>";

This line contains php code, that will only get rendered on page load. If you refresh the page and view the source you will see i has updated.

Not sure what you are trying to achieve, but this is a logic errer

EDIT as per your comment

You can return the value from check.php:

<? 
if($_POST){
    $_SESSION['disp'] = $_POST['theva'];
    echo 'Session value is now: '.$_SESSION['disp'];
}
?>  

And alter your js success function to alert the data:

success: function(data) {

         alert(data);

     });