Promises

promises.js

const push = results => res => {
  results.push(res);
  return results;
};

const chainPromises = results => (
  (promise, func) => promise.then(func).then(push(results))
);

const series = (...promises) => promises.reduce(
  chainPromises([]), Promise.resolve()
);

const all = (promises, reduce = series) => reduce(...promises)
  .then(res => ({ res: res.map(r => r.res) }))
  .catch(err => ({ err: err.body && err.body.message || err.message || err }));