async-pool-es7

async-pool-es7.js

async function asyncPool(concurrency, iterable, iteratorFn) {
  const ret = []; // Store all asynchronous tasks
  const executing = new Set(); // Stores executing asynchronous tasks
  for (const item of iterable) {
    // Call the iteratorFn function to create an asynchronous task
    const p = Promise.resolve().then(() => iteratorFn(item, iterable));
    
    ret.push(p); // save new async task
    executing.add(p); // Save an executing asynchronous task
    
    const clean = () => executing.delete(p);
    p.then(clean).catch(clean);
    if (executing.size >= concurrency) {
      // Wait for faster task execution to complete 
      await Promise.race(executing);
    }
  }
  return Promise.all(ret);
}

Why not using
p.finally(clean);
instead of
p.then(clean).catch(clean);
?