在文件之间传递变量

Question

I am trying to send information between 2 files.

first file :

function findDepartment(codePostal,commune,deptId)
    {
        if (codePostal.length==5)
        {
        var fichier1 = "inclusions/ajax-cp-departement.php";
           $.ajax({
            url: fichier1,
            data: {codePostal: codePostal, commune: commune},
            success: function(response) {
                $(deptId).val(response);

            },
            error: function(xhr) {
                alert('Error!  Status = ' + xhr.status);
            }
        });
        }
    }

Second file : "inclusions/ajax-cp-departement.php"

$commune = $_REQUEST['commune'];
$commune = trim($commune);
$codePostal= $_REQUEST['codePostal'];
$codePostal= trim($codePostal);

if (strlen($commune)>0 && strlen($codePostal)>0)
{
    // Liste les communes du département demandé
    $query = "SELECT departement
    FROM commune_zone
    WHERE commune LIKE '$commune' 
    AND code_postal LIKE '$codePostal' 
    LIMIT 1";
}

this is how i call my function :

findDepartment(monCp,$("#ville_projet").val(), "#departement_projet");

the commune variable is not detected since it sends an empty result, when i remove commune it works, any ideas why do I have this problem ?