fetcher.js

import fetchPool from "./fetchPool";
const fetch = fetchPool(5);

// const urlfoo = ...fill in the void...

// will never fetch more than 5 at a time
for (var i = 0; i < 100; i++) {
  fetch(urlfoo);
}

fetchPool.js

import Semaphore from "semaphore-async-await";

const fetchPool = poolCount => {
  const lock = new Semaphore(poolCount);

  return async function() {
    await lock.wait();
    const res = await fetch.apply(this, arguments);
    lock.signal();
    return res;
  };
};

export default fetchPool;