ERRORE AJAX

HTML/JAVASCRIPT:
var x=final_transcript;
/*document.cookie= 'cookie_final='+x;
source= langs[select_language.selectedIndex][1][0];
document.cookie= 'cookie_source='+source;

dest=langs[select_language2.selectedIndex][1][0];
document.cookie= 'cookie_dest='+dest;
final_span.innerHTML=linebreak=linebreak(final_transcript);
*/
source=langs[select_language.selectedIndex][1][0];
dest=langs[select_language2.selectedIndex][1][0];

var sorgente= $("#source").val();

var destinatario= $("#dest").val();
var testo=$("#x").val();
alert(testo);
$.post("progettoajax.php", {'sorgente':sorgente, 'destinatario':destinatario, 'testo':testo});
PHP:

 if (isset($_POST['bottone_recupera']))
    {

		$sorgente=$_POST["sorgente"];
		$destinatario=$_POST["destinatario"];
		$testo=$_POST["testo"];
		echo "<script type='text/javascript'>alert('$sorgente');</script>";
		echo "<script type='text/javascript'>alert('$destinatario');</script>";
		echo "<script type='text/javascript'>alert('$testo');</script>";