multiple responses Cannot set headers after they are sent to the client - node.js

Question

I wrote the following signup function.
It works fine with Postman but when I've added the code between "//send the cookie with the token" and "// end", I got this error message : "(node:11748) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client".
From what I saw here in stackoverflow, this error occurs because of multilple res. but I can't find how to rearrange the code so that I avoid this error.
exports.signup = async(req, res) => {
const { firstName, familyName, email, password, role } = req.body;
console.log("image", req.file);
try {
const user = await User.findOne({ attributes: ['email'], where: { email: email } });
if (user) {
fs.unlinkSync(req.file.path);
return res.status(409).send('This email already exists!');
} else {
const hashPass = await bcrypt.hash(password, 10);
const userObject = {
firstName: firstName,
familyName: familyName,
email: email,
password: hashPass,
role: role,
photoUrl: req.file ? `${req.protocol}://${req.get('host')}/images/${req.file.filename}` : null,
};
console.log("photo", userObject.photoUrl);
console.log("userObject", userObject);
const createdUser = await User.create(userObject);
const newToken = jwt.sign({ userId: user.id },
process.env.COOKIE_KEY, { expiresIn: "24h" }
);
const newCookie = { token: newToken, userId: createdUser.id };
const cryptedToken = cryptojs.AES.encrypt(JSON.stringify(newCookie), process.env.COOKIE_KEY).toString();
res.cookie('snToken', cryptedToken, {
httpOnly: true,
maxAge: 86400000 // 24h
});
res.status(200).send({ message: 'The user is successfully connected!', data: createdUser, cryptedToken: cryptedToken });
}
} catch (error) {
return res.status(500).send({ error: 'An error has occured while trying to sign up!' });
}
}

Answer 1

It's not related to "multiple request". In a successful case (also on error), you wrote status more than once.
for example in a successful case:
first you returned 201 after creating the user (which returned a response to the client)
res.status(201).send({message: User ${req.userObject.firstName} ${req.userObject.familyName} was registred }, createdUser);
and then
and here you tried to send another response at the end of the request
res.status(200).send({ message: 'The user is successfully connected!', data: user, cryptedToken: cryptedToken });
and you got the right error Cannot set headers after they are sent to the client, since it already returned 201 after Creation.
try to do something like:
try {
const hashPass = await bcrypt.hash(password, 10);
const userObject = { firstName: firstName,
familyName: familyName,
email: email,
password: hashPass,
role: role,
photoUrl: req.file ? `${req.protocol}://${req.get('host')}/images/${req.file.filename}` : null,
};
console.log("photo", userObject.photoUrl);
console.log("userObject", userObject);
const createdUser = await User.create(userObject);
//send the cookie with the token
const newToken = jwt.sign({ userId: user.id },
process.env.COOKIE_KEY, { expiresIn: "24h" }
);
const newCookie = { token: newToken, userId: user.id };
const cryptedToken = cryptojs.AES.encrypt(JSON.stringify(newCookie), process.env.COOKIE_KEY).toString();
res.cookie('snToken', cryptedToken, {
httpOnly: true,
maxAge: 86400000 // 24h
});
res.status(200).send({ message: 'The user is successfully connected!', data: user, cryptedToken: cryptedToken });
}
catch (error) {
return res.status(500).send({ error: 'An error has occured while trying to sign up!' });
}