How to flash messages from inside promises in node.js?

Question

How can we flash messages in node.js from inside promises? I used the library connect-flash https://github.com/jaredhanson/connect-flash .

The following code doesn't work:

Patient.findOne({
    hospitalNumber
}).then((patient) => {
    if (_.isEmpty(patient)) {
        throw Error('Patient does not exist');
    }
    res.status(200).render('patientPage');
}).catch((err) => {
    console.log(err);
    req.flash('error_msg', "Something went wrong.");
    res.redirect(400, '/app');
});

Answer 1

well, according to the library docs:

req.flash('blah')

your code has res.flash

req ==! res

:)

I hope it helps you!

Answer 2

connect-flash is just a kind of store for messages. You still need to provide them to the render and render them yourself.

So add them to the render call...

res.redirect(400/*?*/, '/app', { messages: req.flash('error_msg') });

...and place them on your template (here assuming you use pug):

p= messages

It is worth mentioning that flash() returns an array of messages, even when you flash only once . So, to have better control you may use something like:

each message in messages
    p= message

Finally there is no special handling of flashes within promises. Everything you flash will be available to the renderer. So you could change your code to:

Patient.findOne({
    hospitalNumber
}).then((patient) => {
    if (_.isEmpty(patient)) {
        req.flash('error', 'Patient does not exist');
        throw Error('Patient does not exist');
    }
    res.status(200).render('patientPage');
}).catch((err) => {
    console.log(err);
    res.redirect(400, '/app', { errors: req.flash('error') });
});

or, better yet (but without flash, note error instead of errors ):

Patient.findOne({
    hospitalNumber
}).then((patient) => {
    if (_.isEmpty(patient)) {
        throw Error('Patient does not exist');
    }
    res.status(200).render('patientPage');
}).catch((err) => {
    console.log(err);
    res.redirect(400, '/app', { error: err.message });
});