Should I use Ajax POST or GET to create an element in the DB and getting the created ID with Node.JS?

I want to add a new element in my Database and i'd like to get the created Id. (using node.js)

At the moment, I use an Ajax Post to add the element in the DB but I can't figure how to get the returning ID.

Should I use a GET or is there a way to get the id with my POST ? What is the best practive ?

Here's some code samples:

Client Script:

ajaxPost('/newElement', element, function(idDB) {
        alert(idDB); //it says undefined
    });

function ajaxPost(path, data, callback) {
  $.ajax('http://'+ url + path, {
    type: 'POST',
    data: JSON.stringify(data),
    contentType: 'application/json',
    success: function() { if ( callback ) callback(); },
    error  : function(XMLHttpRequest, textStatus, errorThrown) { if ( callback ) callback(); }
});
}

Server

app.post('/newElement', function(req, res) {
    queryDB.InsertElement(client, req.body, function(err, idDB) {

        if (err) {
            console.error(err);
            res.end();
        } else {
            console.log(idDB); //I have the returned id here...
            res.send(idDB);
        }

    });
});

Many Thanks.