How to correctly add data to the session after returning a response to the client in node+express?

Question

Node.js

Like this - it works, but waits for the timeout to end:

app.post('/sessionTest/', urlencodedParser, function (req, res) {
  var sess = req.session;
  console.log(sess);
  if (!req.body.key) {
    return res.sendStatus(400);
  }
  setTimeout(()=>{
    sess[req.body.key] = Math.random();
    return res.send('Sucess!');
  },1000);
});

in this way the result is returned immediately, but nothing is saved to the session

app.post('/sessionTest/', urlencodedParser, function (req, res) {
  var sess = req.session;
  console.log(sess);
  if (!req.body.key) {
    return res.sendStatus(400);
  }
  setTimeout(()=>{
    sess[req.body.key] = Math.random();
  },1000);
  return res.send('Sucess!');
});

I just would like to return control to the client before all the processing is over and some data becomes known, which then needs to be saved to the session

Answer 1

in fact, the chest just opened: in case of modifying the session data after returning the response, you just need to call sess.save ()

Answer 2

in the first option, set the delay to zero in settimeout, because it will still work only after the call stack has been emptied.