Promise patterns

promisePatterns.js

const _ = require('lodash');

function series(arr, fn) {
  let result = [];

  return _.reduce(arr, (acc, item) => {
    acc = acc
      .then(() => fn(item))
      .then(res => result.push(res));
    return acc;
  }, Promise.resolve())
    .then(() => result);
}

function all(arr, fn) {
  let promises = _.map(arr, item => fn(item));
  return Promise.all(promises)
}

function chunks(arr, fn, chunkSize) {
  let result = [];
  return _.chain(arr)
    .chunk(chunkSize)
    .reduce((acc, chunk) => {
      acc = acc
        .then(() => all(chunk, fn))
        .then(res => result = result.concat(res));
      return acc;
    }, Promise.resolve())
    .value()
    .then(() => result);
}

module.exports = {
  series,
  all,
  chunks
};