Effective approach to processing items in batches asynchronously in JavaScript. This function processByBatches allows parallel processing of items, with a customizable batch size. There's room for enhancements, like incorporating Promise.allSettled or adding more options. Feedback and improvements are welcome!

processByBatches.ts

interface ProcessByBatchesOptions {
  /**
   * The number of items to process in parallel.
   * @default 10
   */
  batchSize?: number
}

async function processByBatches<ItemType, ResultType>(
  items: ItemType[],
  callback: (item: ItemType) => Promise<ResultType>,
  options: ProcessByBatchesOptions = {},
): Promise<ResultType[]> {
  const { batchSize = 10 } = options
  const batches = []
  for (let i = 0; i < items.length; i += batchSize)
    batches.push(items.slice(i, i + batchSize))

  const maybePromise: Promise<ResultType[]>[] = []

  for (const batch of batches)
    maybePromise.push(Promise.all(batch.map(callback)))

  return Promise.all(maybePromise).then(results => results.flat())
}