Question

In my Node.js application, I have a function (routed by Express) which presents a form to the user:

app.get('/register', function (req, res) {
  res.render('form');
});

I have another function, routed to the same URL, but which handles POST requests, which receives the data submitted by the previous form. If the form does not validate, it redirects the user back to the form; otherwise, it does what should be done:

app.post('/register', function (req, res) {
  if (validate(req.registerForm)) return res.redirect('back');
  persistStuff(req.registerForm, function (err, data) {
    // Do error verification etc.
    res.redirect('back')
  });
});

What I want to do is to send a error message to be presented, in the line:

if (validate(req.registerForm)) return res.redirect('back');

To write something like

if (validate(req.registerForm)) return res.render('form', {msg:'invalid'});

is unacceptable because I want to follow the POST-REDIRECT-GET pattern. I could do something like

if (validate(req.registerForm)) return res.redirect('/register?msg=invalid');

but it would hardcode an URL in my code and I’d prefer to avoid it. Is there another way to do it?

Answer 1

You need to use flash notifications, and it is built into express.

You’ll add a message like so: req.flash("error", "Invalid form...");

You’ll need a dynamic handler to add the messages to your rendered template, or you can check out the ones TJ has made for express. (express-messages)