NODE检索表单变量

I am French and no one in English so everything is translated by google! I am a beginner on NODE.

In my index.html file, there is a form that I send to the server via $ .ajax with the POST method

To retrieve this form on the server

app.post('/connexion', function (req, res) {
 
    var postData = '';
    var pathname = url.parse(req.url).pathname;
        console.log('Reçue: '+ pathname +' .');
        req.setEncoding('utf8');
        req.addListener('data', function(postDataChunk) {
            postData += postDataChunk;
            console.log('POST reçu ' + postDataChunk +'.');
        });

and on the console, I receive this in return

Reçue: /connexion .
POST reçu -----------------------------4511735334446617171533446239
Content-Disposition: form-data; name="pseudo"
 
Nath
-----------------------------4511735334446617171533446239
Content-Disposition: form-data; name="mdp"
 
moi
-----------------------------4511735334446617171533446239--
.

But I do not find how to retrieve the values of the variables pseudo and mdp.

Can you help me understand and recover these values?

Thank you for your help

</div>

"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.