Promises Have Methods To Help With Concurrency

Promises come with a few interesting methods that can allow for engineers to manage multiple async operations: Promise.all() and Promise.allSettled() will be covered here.

A Bit About Concurrent, Parallel, and Synchronous

These 3 words can be a bit convoluted: concurrent, parallel, and

Promise.all For Getting 1 Promise For All Promises

Compared to the previous examples where promises are written and ran one-at-a-time, here is a much simpler to write syntax that, more or less, does the same thing...

const { readFile, readdir } = require('fs').promises;

const FILES_DIR = './../files';

const print = (data) => {
  console.log(Buffer.concat(data).toString());
};

function readFilesAndStart(files) { 
  const readFilePromises = files.map((f) => readFile(`${FILES_DIR}/${f}`));
  return Promise.all(readFilePromises).then(print).catch(console.error);
}
readdir(FILES_DIR).then(readFilesAndStart).catch(console.error);

Promise.all...

• takes a list (array) of promises. Here, that list of promises comes from the files.map((f) => readFile('${FILES_DIR}/${f}')) function which returns a list of promises
• resolves, "completes", when all of the promises in the array are done