Where can I see the Set Cookie header on the server set with express-session?

Question

In postman when I make a request to my server I get these response headers:

Connection: keep-alive
Content-Length: 3
Content-Type: text/html; charset=utf-8
Date: Wed, 02 Dec 2020 21:52:10 GMT
ETag: W/"3-f1UKn0xEFzo3Zk2TjxNV8PkqR6c"
Set-Cookie: connect.sid=s%3AHQ54fVZ7KP9jrPKP1j8Z93O8bIXN0CJl.lTSlYwA48TgarO7MtXGFiG1JL%2FPOHe%2FSGV0cqikGGU4;
Path=/; HttpOnly
X-Powered-By: Express

How do I see these headers in express? I paused the server for this request right before res.send('hey') but all I got was one header:

res.getHeaders()
{x-powered-by: 'Express'}

I specifically want to see the cookie that the server is sending to the browser. How can I see all the response headers in express while debugging?

Server file:

const express = require('express');
const session = require('express-session');

const app = express();

app.use(
  session({
    secret: 'very secret 12345',
  })
);

app.use(async (req, res, next) => {
  req.session.visits = req.session.visits ? req.session.visits + 1 : 1;
  console.log(`${req.method}: ${req.path}`);
  console.log('req.headers.cookie: ', req.headers.cookie);
  next();
});

app.get('/sayhi', (req, res, next) => {
  res.send('hey');
});

app.listen(4001).on('listening', () => {
  console.log('info', `HTTP server listening on port 4001`);
});

Answer 1

Because Content-Type Set-Cookie header is set after you called res.send(), so you need to add event listener to listen when the response close.
Then you could see what headers this response have.
But, it's a callback function after response sent, so you could just only look what value sent in this response.

app.get('/sayhi', (req, res, next) => {
    res.on("close", function() {
        console.log("====== close event =======");
        console.log(res.getHeaders());
        console.log("====== close event =======");
    })
    res.send('hey');
});

By the way, you could also use DEBUG=* node your_server.js to look some debug message implemented by other libraries.