Alert on ajax succes and error

	<table align=center>
	<form method="POST" action="" align="center" >
	<tr colspan="2">
	<td colspan="2" align=center><span style="color:#ff80aa;font-size:30px;" style="padding-bottom:50px;" > edition du profil:</span></td>
	</tr>
	<tr style="padding-bottom:50px;">
	<td><label style="color:#ff80aa;font-size:25px;"> Nom: </label></td>
	<td><input type="text" name="newnom" id="nom" placeholder="nom" value="<?php echo $user['nom']; ?>"></input></td>
	</tr>
	<tr style="padding-bottom:50px;">
	<td><label style="color:#ff80aa;font-size:25px;" > Prenom: </label></td>
	<td><input type="text" name="newprenom" id="prenom" placeholder="prenom" value="<?php echo $user['prenom']; ?>"></input></td>
	</tr>
	<tr style="padding-bottom:50px;">
	<td><label style="color:#ff80aa;font-size:25px;" > adresse:</label></td>
	<td><input type="text" name="newadresse" id="adresse" placeholder="adresse" value="<?php echo $user['adresse']; ?>"></input></td>
	</tr>
	<tr style="padding-bottom:50px;">
	<td><label style="color:#ff80aa;font-size:25px;"> email:</label></td>
	<td><input type="text" name="newmail" id="mail" placeholder="mail" value="<?php echo $user['email']; ?>"></input></td>
	</tr>
	<tr style="padding-bottom:50px;">
	<td><label style="color:#ff80aa;font-size:25px;" id="tel"> tel:</label></td>
	<td><input type="text" name="newtel" id="tel" placeholder="tel" value="<?php echo $user['tel']; ?>"></input></td>
	</tr>
	<tr style="padding-bottom:50px;" >
	<td colspan="2" align=center><input type="submit" value="mettre à jour" onclick="mettre_a_jour();"></input></td>
	</tr>
	
	</form>
	</table>

<script>
function mettre_a_jour(){
	$.ajax({
		type: "post",
		url: "mise_a_jour.php",
		data: {id_client: $_GET["id_client"] ,nom: $("#nom").val(), prenom: $("#prenom").val(), mail: $("#mail").val(), tel: $("#tel").val(), adresse: $("#adresse").val()},
		success: function(){
			return alert('changement enregistré');
		},
		error: function(){
			return alert('inexistante');
		}
		
	});
}
</script>

<?php
$bdd= new PDO('mysql:host=localhost;dbname=magasin','root','');
nom = $_POST['nom'];
prenom = $_POST['prenom'];
tel = $_POST['tel'];
adresse = $_POST['adresse'];
email = $_POST['mail'];
id_client= $_POST["id_client"];
	$query="UPDATE clients SET nom='{nom}' prenom='{prenom}' tel='{tel}' adresse='{adresse}' email='{email}' WHERE id_client='{id_client}'";
	$stm1=$bdd->prepare($query);
	$stm1->execute();
?>