Map & Reduce promises with concurrency throttling - an example

gistfile1.txt

const pReduce = require('p-reduce');
const pMap = require('p-map');
const delay = require('delay');

// const batches = [['a'], ['b', 'c'], ['d', 'e', 'f', 'g'], ['h'], ['i'], ['j', 'k']];
const batches = [['a', 'b', 'c', 'd', 'e', 'f', 'g'], ['h'], ['i'], ['j', 'k']];

const step = 2000;
const max = 5000;

const start = Date.now();
const concurrency = 3;

pReduce(batches, async (sum0, batch) => {
  console.log(`------ ${Date.now()- start}`);
  const result = await pMap(batch, async child => {
    const t = step + Math.random() * max;
    console.log(`processing '${child}' ${t} ${Date.now()- start}`);
    await delay(t);
    console.log(`completed '${child}'`);
    return child;
  }, { concurrency });
    return result.reduce((sum1, r) => {
      return sum1 = `${sum1}${r},`;
    }, sum0);
}, '>>').then(result => console.log(result)).catch(err => console.log(`ERROR: ${err}`));