Promise runner example for sgmonda.com

promiseRunnerExample.js

// Usage: $ node promiseRunnerExample.js <mode>
// Where <mode> can be one of the following: 'serie', 'parallel', 'parallelLimit'

const numbers = Array(50).fill(1).map((_, index) => index);

const getNumber = (num) => new Promise((resolve) => {
  const delay = Math.random() * 1000;
  const fun = () => resolve(num);
  setTimeout(() => {
    process.stdout.write(`${num}, `);
    fun();
  }, delay);
});

async function runInSerie() {
  for (const num of numbers) await getNumber(num);
  console.log("Finished");
}

async function runInParallel() {
  const promises = numbers.map(getNumber);
  await Promise.all(promises);
  console.log("Finished");
}

async function promiseRunner(funs, concurrency) {
  let result = [];
  while (funs.length > 0) {
    const group = funs.splice(0, concurrency);
    const promises = group.map(f => f());
    const partial = await Promise.all(promises);
    result = result.concat(partial);
  }
  return result;
}

async function runInParallelLimit(concurrency) {
  const promiseCreators = numbers.map(num => () => getNumber(num));
  await promiseRunner(promiseCreators, 5);
  console.log("Finished");
}

(async () => {
  const mode = process.argv[2];
  if (mode === 'serie') await runInSerie();
  else if (mode === 'parallel') await runInParallel();
  else if (mode === 'parallelLimit') await runInParallelLimit(5);
})()