parallelize-generator-promises

A simple utility to run promises yielded by a generator in parallel. This is incredibly useful when you need to run a bunch of tasks as fast as possible without waiting for one another.

Installation

parallelize-generator-promises is available on both npm and JSR.

To use from npm, install the parallelize-generator-promises package and then import into a module:

import { parallelizeGeneratorPromises } from "parallelize-generator-promises";

To use from JSR, install the @reda/parallelize-generator-promises package and then import into a module:

import { parallelizeGeneratorPromises } from "@reda/parallelize-generator-promises";

Polyfilling Promise.withResolvers

If you are using Node.js v20 or below, you will require a polyfill for Promise.withResolvers.

A polyfill for this is available in a separate export as part of this package. To use the provided polyfill, import it at the entrypoint of your application.

npm:

import "parallelize-generator-promises/promise-with-resolvers-polyfill";

jsr:

import "@reda/parallelize-generator-promises/promise-with-resolvers-polyfill";

Usage

import { parallelizeGeneratorPromises } from "parallelize-generator-promises";

async function* getAllProductDetails() {
  for (let page = 1; page <= 100; page++) {
    const products = await fetch(`/products?page=${page}`).then((res) =>
      res.json()
    );
    yield products.map((product) =>
      fetch(`/product/${product.id}/details`).then((res) => res.json())
    );
  }
}

for await (
  const productDetails of parallelizeGeneratorPromises(
    getAllProductDetails(),
  )
) {
  console.log(productDetails);
}

The above example will fetch all product details for one page of products at a time as fast as possible, yielding the product details in the fastest order possible to keep the iterator fed.

If a concurrency limit is required, this utility pairs very well with a semaphore library such as async-sema.

Options

Name	Description
maxBufferedPromises	Limits the maximum number of promises that can be buffered at any given time. Useful to manage memory usage in the case where you are generating a lot of promises that aren't being consumed at a fast enough rate. NOTE: this value must be greater than or equal to 1. By default this is undefined which means there is no limit set.