Run JS promises in parallel with limited concurrency

limit.mjs

/*
// Usage example:

async function scrapeUrl() {
  // ...
}
const urls = ['http://foo.com', 'http://bar.com', 'more URLs...'];

// Scrape all URLs with maximun 10 in parralel.
const scrapeUrlLimit = limit(10, scrapeUrl);
await Promise.all(urls.map(scrapeUrlLimit));
*/

import {setTimeout} from 'node:timers/promises';

export function limit(max, fn, delay = 100) {
  let cnt = 0;

  return async function (...args) {
    while (cnt >= max) {
      await setTimeout(delay);
    }

    cnt++;

    try {
      return await fn(...args);
    } finally {
      cnt--;
    }
  }
}