Concurrency

1// mapWithConcurrency — run `fn` over `items` with at most `limit` in flight at
2// once. Preserves input order in the result array regardless of completion order.
3export async function mapWithConcurrency(items, limit, fn) {
4  const results = new Array(items.length);
5  let next = 0;
6  async function worker() {
7    while (next < items.length) {
8      const i = next++;
9      results[i] = await fn(items[i], i);
10    }
11  }
12  await Promise.all(Array.from({ length: Math.min(limit, items.length) }, worker));
13  return results;
14}