bluebird-map.js

const bluebird = require('bluebird');

async function task(data, ms = 500) {
  console.log(data);
  await bluebird.delay(ms);
  return data;
}

bluebird.map(['A', 'B', 'C', 'D', 'E', 'F'], async (item) => {
  return task(item);
}, { concurrency: 3 }).then((result) => {
  console.log(result);
});