Run concurrent tasks with limit in TypeScript

limit-concurrency.ts

type TaskFn<T> = () => Promise<T>;

// see: https://maximorlov.com/parallel-tasks-with-pure-javascript/
async function limit<T>(tasks: TaskFn<T>[], concurrency: number) {
  const results: (T | Error)[] = [];

  async function run(iterator: IterableIterator<[number, TaskFn<T>]>) {
    for (const [index, task] of iterator) {
      try {
        results[index] = await task();
      } catch (error) {
        results[index] = new Error(`Failed with: ${(error as Error).message}`);
      }
    }
  }

  const workers = new Array(concurrency).fill(tasks.entries()).map(run);

  await Promise.allSettled(workers);

  return results;
}