batch-map.js

const { curry, splitEvery } = require("ramda");

const batchMap = curry((batchSize, fn, list) =>
  splitEvery(batchSize, list)
    .map(batch => all => Promise.all(batch.map(fn)).then(res => all.concat(res)))
    .reduce((results, batch) => results.then(batch), Promise.resolve([]))
);

module.exports = batchMap;

example.js

const batchMap = require("batch-map");

const delay = interval => new Promise(res => setTimeout(res, interval));

Promise
  .resolve([1, 2, 3, 4, 5, 6])
  .then(batchMap(2, n => delay(1000).then(() => n * 10)))
  .then(console.log);

// Will print [10, 20, 30, 40, 50, 60] after 3 seconds