Dealing with error in bcrypt.compare callback

I would expect it to be

bcrypt.compare(password, user.password, function(error, result) {
        if(result === true) {
          return callback(null, user);
        }
        else {
          return callback(error);
        }
}

We don't need to differentiate between having an error or the passwords not matching, maybe except for the status codes.

In any case, I don't know why the error is not passed in the callback in the video.

I think the reason why the error is not passed in the callback is because passing parameters in JavaScript is optional. So by not passing in anything, the error and result parameters become undefined.

If you notice in the video in the index.js file, we set up the if conditional to check if there is an error or if there is no user:

if(error || !user){
        var err = new Error('Wrong email or password.');
        err.status = 401;
        return next(err);
}

Since both error and user are undefined, error evaluates to false, but !user evaluates to true, so the if conditional statement is true and the block of code runs.