promise-vs-async-callbacks.js

// Assume our api does not want these fields returned (ideally we would strip from db query, but you get the idea)
var cleanseData = R.map(R.omit('dob', 'social-security', 'nickname', 'height', 'favourite-movie'));

const age = 25;

// Remove users below an age
var filterData = R.filter((u) => { return u.age >= age });

function getUsersOlderThanAge (age) {  
  // We could add a catch here if we want to add more error data...
  return http.get('http://api.users.com/users.json')
    .then(filterData);
}

return Promise.resolve() // starts a chain, any subsequent code if it "throws" will be caught safely
  .then(() => getUsersOlderThanAge(age))
  .then((users) => cleanseData(users))
  .catch((e) => {
    log.error(new VError(e, 'failed to get users'));
  });


// And now with callbacks...................

function getUsersOlderThanAge (age, callback) {  
  return http.get('http://api.users.com/users.json', function (err, res) {
    if (err) {
      callback(err);
    } else {
      callback(null, filterData(res));
    }
  })
}

async.waterfall([
  function (next) {
    getUsersOlderThanAge(age, next)
  },
  function (users, next) {
    next(null, cleanseData(users))
  }
], (e, res) => {
  if (e) {
    log.error(new VError(e, 'failed to get users'));
  }
});