User promise

UserPromise.js

exports.createOrAddUserPromise = (req, res, next) => {
  User.findUserPromise(req.body)
    .then(user => {
      if (user) {
        const existingUser = new User(user);
        return newUser.updatePromise(req.body)
      }
      const newUser = new User();
      return newUser.savePromise(req.body);
    })
    .then(data => res.send(data))
    .catch(e => next(e));
}