Poster des données en ajax vers php

var url = 'pages/fonction-chat.php';
var act = 'ajoutmsg';
$(document).ready(function(){ 
$('.tchat').submit(function(){
       
     var pseudo = $('.form-control').val(); // on sécurise les données
     var message = $('.msg_input').val();

    if(pseudo != "" && message != ""){ // on vérifie que les variables ne sont pas vides
       $.post(url,{action:act,pseudo:pseudo,message:message},function(data){
   if(data.erreur == 'ok'){
    alert('ok');
   }else{
    alert(data.erreur); 
   }

  },'json');
    }
 return false;
 });
 });

<?php
require_once 'pages/connect.php';

$d = array();

 $psd = $_POST['pseudo'];
    $msg = $_POST['message']; // on sécurise nos données
 $_SESSION['pseudo'] = $_POST['pseudo'];
 
 if($_POST['action'] == "ajoutmsg"){
   $msg = htmlentities($message);
   $req = $pdo->prepare("INSERT INTO message (pseudo, message, date) VALUES ( :psd, :msg, NOW())");
   $req->execute(array(':psd'=>$psd, ':msg'=>$msg));
   $d['erreur'] = 'ok';
 }
echo json_encode($d);
?>

<form method="post" class="tchat">
 <?php if(!empty($_SESSION['pseudo'])): ?>
  <div class="chat_body">
    <?php
    $req =$pdo->prepare("SELECT message, date FROM message WHERE pseudo =:psd ORDER BY Date ASC");
    $req->execute(array(':psd'=>$_SESSION['pseudo']));
    $result=$req->fetchAll();   
    ?>
   <div class="chat_body">
   <?php foreach ($result as $res):?>
    <div class="msg2">
     <?= $res->message; ?>
    </div>
   <?php endforeach; ?>
   </div>
  </div>
 <?php else: ?>
 <div class="form-group">
  <input class="form-control" placeholder="pseudo" type="text" name="pseudo">
 </div>
 <div class="chat_body" style="height:200px;">
  <div class="msg_insert">
  </div>
 </div>
 <?php endif;  ?>
 <div class="chat_foot">
  <textarea class="msg_input" placeholder="Message" rows="3" name="message"></textarea>
  <button type="submit" class="btn btn-primary form-control"><span class="glyphicon glyphicon-send"></span></button>
 </div>
</form>