Node JS Request Response not working - node.js

Question

This is my register route. If the registration is successful I want to redirect to the secret route. But the response is not working. When it is successful the page keeps loading and loading and doesn't redirect me to the secret route.
app.post('/register', function(req, res) {
User.create({
username: req.body.username,
password: req.body.password,
email: req.body.email
}, function(err, result, res) { **HERE**
if(err) throw err;
res.redirect('/secret');
console.log(result);
});
});
I tried this and the /secret route works but when I do this it doesn't check for registration errors and immediately redirects to the secret route.
app.post('/register', function(req, res) {
User.create({
username: req.body.username,
password: req.body.password,
email: req.body.email
}, function(err, result) { **HERE**
if(err) throw err;
console.log(result);
});
res.redirect('/secret');
});
I tried to add return err. So if there is an error the function will exit.
But here the /secret route still is still shown when I intentionally made an error in the registration. So the return is not exiting the function.
app.post('/register', function(req, res) {
User.create({
username: req.body.username,
password: req.body.password,
email: req.body.email
}, function(err, result) {
if(err) return err; **TRIED RETURN TO EXIT**
});
res.redirect('/secret');
});

Answer 1

That it keeps loading and loading indicates that the create user function returns an error in the callback. Or an error occured in the callback.
In case of an error no reponse might be send which will result in a dangling request.
In your code the reason is that you have to remove the res from the create user callback otherwise you will hide the original res of the middelware callback, which will result in an error. But you also have to handle the case when create user itself results in an error.
Your callback could look that way:
function(err, result) {
if(err) {
res.status(500).send('an error occured')
} else {
res.redirect('/secret');
console.log(result)
}
}
How exaclty the callback should look like depends on what you want to do in case of the error. You also might want to choose a different error code then 500 that would match better.

Answer 2

I believe you're confusing the callback-based nature of asynchronous programming in normal NodeJS with regular sequential programming.
The call to User.create will return immediately, and lines following it execute prior to anything within the callback you provide. So your res.redirect() call will trigger the immediate response of a redirect to the client. When the callback finally runs, the request has finished.
Instead, you will want to perform the redirection inside of the callback function, after checking for potential errors.
Your code should end up looking like this:
app.post('/register', function(req, res) {
User.create({
username: req.body.username,
password: req.body.password,
email: req.body.email
}, function(err, result) {
if(err) throw err;
// Since we got here, things went well presumably
res.redirect('/secret');
});
});