Show HN: Promise.allSettled Alternative with Concurrency Support

4 months ago 10

Settle Map is a tool that combines the features of Promise.allSettled and Array.map. It simplifies the process of mapping promises, providing results flexibility with hassle free error handling and lets you control how many can run at the same time using concurrency. In other words, it will help you prevent being rate-limited.

import { settleMap } from "settle-map"; const items = [ "https://example.com", "https://news.ycombinator.com", "https://github.com", "https://stackoverflow.com", ]; const settled = settleMap( items, // your items async (item, index) => { // your async map function - fetch URL and get status const response = await fetch(item); if (!response.ok) { throw new Error(`Failed to fetch ${item}: ${response.status}`); } return { url: item, status: response.status, content: await response.text(), }; }, 2 // the concurrency you want to set ); // or import { createSettleMap } from "settle-map"; // use this map function all over the place with same options const map = createSettleMap({ concurrency: 2 }); const settled = map(items, asyncMapFunction); // even you could override the default options. like below the concurrency will changed from 2 to 5 const result = await map(item, asyncMapFunction, 5);

Get live response by listening events

Get response value on resolve any item immediately

settled.on("resolve", ({ value, item, index }) => { // your actions });

Catch error immediately on reject any item

settled.on("reject", ({ error, item, index }) => { // your actions });

Get response immediately on retry any item

settled.on("retry", ({ error, item, index, tried }) => { // your actions });

Get the final result object

The complete event will not be emitted when omitResult options will be true.

settled.on("complete", ({ values, error }) => { // your actions });

Note

Each event can only trigger one function. If you try to set up multiple listeners for the same event, the most recent one will replace any earlier ones.

Get the final result at once

To wait and get all result at once you just have to add await keyword like casual async/await approach or invoke the then method.

const result = await settled; // An universal promise like syntax that returns only resolved response /* output { values: [1, 3, 5], errors: PayloadError[] // this errors returns array of error with payload { item, index } so you could know where the error happened } */

Wait Until All Processes Are Done

If you want to wait until all processes are done, you can use the waitUntilFinished method.

await settled.waitUntilFinished(); // will return always a resolved promise

Abort all process when you need

you could abort the all remaining processes any time and get the current result using abort method

const result = settled.abort();

you could watch the updated status using status method that will return the number of active and pending process

const status = settled.status(); console.log(status); /* { activeCount: number pendingCount: number } */

Retry options on reject or fail promises

You could specify a retry limit and delay for each promise, in case it fails or is rejected.

const options = { concurrency: 2, onFail: { attempts: 3, // the number of attempts on fail delay: 2000, // ms }, omitResult: true, // the final result will be undefined incase it's true. }; const settled = settleMap(items, asyncMapFunction, options);

settleMap(items, fn, options)

A function that settles promises returned by the provided function (fn) for each item in the items array. The promises are settled according to the provided options.

items (T[]): An array of items to be processed.
fn ((item: T, index: number) => Promise<R>): A function that takes an item and its index as parameters and returns a Promise.
options (SettleOptions | number): An object that specifies the concurrency and retry options. If a number is provided, it is treated as the concurrency level. Default is 1

Returns an object with the following methods:

waitUntilFinished(): A method that returns a promise that resolves when all items have been processed, regardless of whether they succeeded or failed.
status(): A method that returns the current status of the settling process.
on(event, listener): A method that allows you to listen for certain events.
abort(): A method that aborts all remain processes and return the current result.

Note

Since the return value has then method so the settleMap function is awaitable. Followed the Thenable approach. see MDN

A curry function of settleMap that will help you to set default options and use the map function with same option everywhere. even you could modify the options for each individual use.