JsHttpRequest не работает (при выборе в select ничего не происходит)

<script type="text/javascript" src="scripts/JsHttpRequest.js"> </script>
<script type="text/javascript"> 
  
  function selformob()
{
// Создаем новый JsHttpRequest объект
var req = new JsHttpRequest();
req.onreadystatechange = function() {
if (req.readyState == 4)
{
var response = req.responseText;
document.getElementById("t").innerHTML = response;
}
}
req.open(null, 'selformob.php', true);
// Send data to backend.
var fak = document.getElementById("sel_fak").options[document.getElementById("sel_fak").selectedIndex].value;
req.send( { val: fak } );
return false;
}
}
  
</script>
 
<?php
include("config.php");
 
header("Content-Type: text/html; charset=utf-8");
 
echo '<div style="background: #E6E6FA; padding: 10px;" name="heah" id="head">';
 
    $query = 'SELECT  DepartmentCode, Name FROM  department ORDER BY departmentcode';
    $res = mysql_query( $query );
    echo 'Факультет: <select class="sel_font" name="sel_fak" id="sel_fak" onchange="selformob()">'; 
        while ( $fak = mysql_fetch_array( $res ) ) {
            echo '<option value="'.$fak['DepartmentCode'].'">'.$fak['Name'].'</option>';
        }
    echo '</select>';
echo '</div><br><div name="t" id="t" style="background-color: blue; height: 50px;"></div>';
?>

<?php
include("config.php");
include("JsHttpRequest.php");
 
$JsHttpRequest = new JsHttpRequest("utf8");
$fak = $_REQUEST['val'];
echo $fak;
exit();
?>

$JsHttpRequest =& new JsHttpRequest("utf8");

$JsHttpRequest = new JsHttpRequest("utf8");