Error: TypeError: Cannot read property 'catch' of undefined when trying to register user for website node.js

Question

I seem to have messed up one of my promises (I think) in a javascript function that is supposed to register a user. I have included the post request and the actual function itself.

app.post("/register", (req, res) => {
    dataServiceAuth.registerUser(req.body).then(() => {
        res.render("register", {successMessage: "User created"});
    }).catch((err) => {
        res.render("register", {errorMessage: err, user: req.body.user});
    });
});



module.exports.registerUser = function (userData) {
    return new Promise(function (resolve, reject) {
        if (userData.password != userData.password2) {
            reject("Passwords do not match");
        }
        else {
            let newUser = new User(userData);

            newUser.save((err) => {
                resolve();
            }).catch((err) => {
                if (err) {
                    if (err.code == 11000) {
                        reject('User Name already taken');
                    }
                    else {
                        reject('There was an error creating the user: ${err}');
                    }
                }
            });
        }
    });
};

Solution

If newUser.save can return a promise, you definitely shouldn’t be passing a callback to it, or even using the Promise constructor at all. If you really want to reject with strings, the way to implement that would be by transforming rejections from newUser.save() with .catch into new rejections by returning them, and returning the resulting promise from registerUser:

module.exports.registerUser = function (userData) {
    if (userData.password != userData.password2) {
        return Promise.reject("Passwords do not match");
    }

    let newUser = new User(userData);

    return newUser.save().catch((err) => {
        if (err.code == 11000) {
            return Promise.reject('User Name already taken');
        }
        else {
            return Promise.reject('There was an error creating the user: ${err}');
        }
    });
};

Comments

[CertainPerformance]

Seems like newUser.save is not returning something catchable, but newUser.save was not posted in your code.

[traktor]

Check if newUser.save is a Node style callback which is passed a falsey value for the err parameter when the operation succeeded, or a non-falsey value (includes non zero numbers) if an error occurred.

[Jasper French]

Awesome looks fixed everything and it looks a lot cleaner as well.