remember-promise

A simple utility to remember promises that were made! It is greatly inspired by the p-memoize utility but with additional built-in features and changes such as:

• ttl expiry
• stale-while-revalidate behavior
• ability to ignore results from being cached
• optimal probabilistic cache stampede prevention
• zero dependencies + tiny bundle size + commonjs, deno and browser support!

Installation

remember-promise is available on both npm and JSR.

To use from npm, install the remember-promise package and then import into a module:

import { rememberPromise } from "remember-promise";

To use from JSR, install the @reda/remember-promise package and then import into a module:

import { rememberPromise } from "@reda/remember-promise";

Usage

import { rememberPromise } from "remember-promise";

const getRedditFeed = rememberPromise(
  (subreddit) =>
    fetch(`https://www.reddit.com/r/${subreddit}.json`).then((res) =>
      res.json()
    ),
  {
    ttl: 300_000, // 5 minutes before the result must be revalidated again
    /* see below for a full list of available options */
  },
);

const firstResult = await getRedditFeed("all");
const secondResult = await getRedditFeed("all"); // this call is cached

Options

Name	Description
ttl	Configures how long in milliseconds the cached result should be used before needing to be revalidated. Additionally, setting this value to zero or a negative number will disable caching. NOTE: the actual revalidation of the cached result is done slightly before expiry by default. This can be adjusted using the xfetchBeta option. By default this is Infinity so the cached result will be used indefinitely.
allowStale	This enables stale-while-revalidate behavior where an expired result can still be used while waiting for it to be updated in the background asynchronously. By default this is set to true so the behavior is enabled.
cache	This is where cached results will be stored. It can be anything you want such as lru-cache or a redis backed cache as long as it implements a get and set method defined in the RememberPromiseCache type. If you would like to disable caching and only deduplicate identical concurrent calls instead then set this to false. When this is set to false, the onCacheUpdateError and shouldIgnoreResult options will be never be used. By default this is a new instance of Map.
getCacheKey	Identical behavior to the cacheKey option in p-memoize except that it's allowed to return a promise. It should return what the cache key is based on the parameters of the given function. By default this will serialize all arguments using JSON.stringify.
onCacheUpdateError	Use this to catch errors when attempting to update the cache or if shouldIgnoreResult throws an error. By default this is undefined which means any errors will be rethrown as an unhandled promise rejection.
shouldIgnoreResult	Determines whether the returned result should be added to the cache. By default this is undefined which means it will always use the returned result for caching.
xfetchBeta	This is the beta value used in optimal probabilistic cache stampede prevention where values more than 1 favors earlier revalidation while values less than 1 favors later revalidation. By default this is set to 1 so the revalidation of a cached result will happen at a random time slightly before expiry. If you wish to opt-out of this behavior, then set this value to 0.