Example of concurrency using Javascript promises + await

Promise.all.js

const sleep = (seconds) => {
  return new Promise((accept) =>
    setTimeout(accept, seconds * 1000, `slept ${seconds}`),
  );
};

async function execParallel() {
  console.log(new Date(), 'starting');
  // promises will execute concurrently, so that execution time = slowest one (not the sum)
  const out = await Promise.all([sleep(5), sleep(5), sleep(5)]);
  console.log(new Date(), 'ended:', out);
}

execParallel().then(console.log);