NODE检索表单变量

"body-parser" works very well to recover variables sent "normally" from a form but I can not retrieve these variables if I send them in post method via $ .ajax Maybe I'm doing my job wrong. On my server file

app.post('/', function(req, res) {
var pseudo = req.body.pseudo;
var mdp = req.body.MdP;

console.log(pseudo);
console.log(mdp);

res.send(true);

});

in the client.js

$('#connect_Chat').on('submit', function (event) {
event.preventDefault();
//on récupère le pseudo et le mot de passe
var pseudo =  $('#login').val().trim();
var mdp = $('#MdP').val();
var formDataConnectUser = new FormData();
formDataConnectUser.append('pseudo', pseudo);
formDataConnectUser.append('MdP', mdp);
$.ajax({
    url: 'https://localhost:8080/',
    type: 'post',
    data: formDataConnectUser,
    processData: false,
    contentType: false,
    success: function(data) {
        if (data === true) {
            $('body').removeAttr('id');
            $('#text-plus-4').modal('hide');
            $('#boutonConnexion').html('<div class="form-group" style="float:right;"><label for="n">Votre pseudo :</label><input type="text" class="pseudoNew" value="'+user.username+'" disabled="disabled"></div>');
            $('#envoi_message').removeAttr('disabled');
            $('#message').removeAttr('disabled');
            $('#message').focus();
        } else {
            alert('Mauvais pseudo ou Mot de Passe !');
        }
    }
});

});

In the server console, variables are displayed as undefined.