Express session not persisting

Question

I'm trying to set up a basic session system in node. Here's what I've got so far:

app.js:

app.use(express.cookieParser('stackoverflow'));
app.use(express.session());

I'm setting the session data in ajax.js:

addClassToCart: function(req, res) {
  req.session.cart = req.body.classId;
  console.log(req.session.cart);
}

This logs the correct information. However, when I try to retrieve that information elsewhere (same file, different function):

console.log(req.session.cart);

I get undefined. I feel like I'm missing something incredibly basic. Various tutorials for this are either awful or require me to add in even more packages (something I'm trying to avoid).

More data from my debugging:

• This works with non-AJAX requests
• The session is set before it's logged.

Answer 1

As it turns out, the issue wasn't with Express' session (as the other answers seem to think). Rather, it was a misunderstanding on my part. I changed addClassToCart to the following:

addClassToCart: function(req, res) {
    req.session.cart = req.body.classId;
    console.log(req.session.cart);
    res.send('class added');
  }

Adding res.send() fixed the problem.

Answer 2

As noted in the answer to a related SO question, this can also occur if you're using fetch to get data from your server but you don't pass in the credentials option:

fetch('/addclasstocart', {
    method: 'POST',
    credentials: 'same-origin' // <- this is mandatory to deal with cookies
})

Cookies won't be passed to the server unless you include this option which means the request's session object will be reset with each new call.