Utility function to sequentially run batches of async operations with configurable concurrency.

async-batch.ts

/**
 * Allows for sequentially running batches of async operations.
 * @param {number} concurrency The maximum number of operations to run concurrently.
 */
export function batch(concurrency: number) {
  return async function <TElement, TResult>(xs: Array<TElement>, handler: (x: TElement) => TResult): Promise<Array<TResult>> {
    const results: Array<TResult> = [];
    const batches = Array.from({ length: Math.ceil(xs.length / concurrency) }, (_, i) => i)

    for await (const batchNumber of batches) {
      const startingIndex = batchNumber * concurrency;
      const elementsToBatch = xs.slice(startingIndex, startingIndex + concurrency);

      const promises = elementsToBatch.map(async (v) => {
        const res = await handler(v);
        results.push(res);
      });

      await Promise.all(promises);
    }

    return results;
  }
}