example how to reduce nesting

less-nested.js

const getUserByEmail = (connection, userEmail) => {
  const userPromise = connection
    .queryAsync(‘SELECT `id` FROM `user` WHERE `email` = ?’, [
      userEmail
    ])
    .then(R.head);
    
  const permissionsPromise = userPromise
    .then(R.unless(R.isNil, (user) => connection
      .queryAsync(‘SELECT `id`, `name` FROM `permission` WHERE `user_id` = ?’, [
        user.id
      ])));
    
  return Promise.all([
    userPromise,
    permissionPromise
  ])
  .then(({user, permission}) => {
    if (!user) {
      return null;
    }
    return {
      user,
      permissions
    };
  });
};