javascript / bluebird: promise batch arrays

promise-batch-arrays.js

import Promise from 'bluebird';

function getBatches(arr, length) {
  let i = 0;
  const result = [];
  while (i < arr.length) {
    result.push(arr.slice(i, i + length));
    i += length;
  }
  return result;
}

function getItems() {
  const arr = '12345678'.split('');
  return Promise.resolve(arr);
}

// All in order
function a() {
  return getItems()
  .then(items => {
    console.log('---');
    items.map(item => console.log('a', item));
  });
}

// Batched
function b() {
  return getItems()
  .then(items => getBatches(items, 3))
  .mapSeries(items => {
    console.log('---');
    items.map(item => console.log('b', item));
  });
}

a().then(b);

usage.txt

$ babel-node promise-batch-arrays.js
---
a 1
a 2
a 3
a 4
a 5
a 6
a 7
a 8
---
b 1
b 2
b 3
---
b 4
b 5
b 6
---
b 7
b 8