promise-memoize

Memoize promise-returning functions. Includes cache expire and prefetch.

• When data expire mode enabled, new values are fetched in advance. Cache will be always valid, without "gaps".
  • Prefetch happens only for items in use. Inactive ones will be GC-ed as usual.
• Errors are not cached
  • You still can enable cache with separate expire time for errors, to avoid specific peak loads. For example, set 120s for good result and 1s on fail.

Install

npm install @forivall/promise-memoize --save

Usage example

// Pseudo code
let db = require('mongoose').createConnection('mongodb://localhost/forum');

function lastPosts(limit) {
  return db.model('Post').find().limit(limit).orderBy('-_id').lean(true).exec(); // <- Promise
}

let cachedLastPosts = require('@forivall/promise-memoize')(lastPosts, { maxAge: 60000 });

// Later...
cachedLastPosts(10).then(posts => console.log(posts));

API

promiseMemoize(fn [, options]) -> memoizedFn

Memoize function fn.

• fn(params...) — function, returning a promise (or any "thenable"). It can have any number of arguments, but arguments should be uniquely castable to strings (see below).
• options — options for memoization (optional)
  • maxAge — an amount of milliseconds it should cache resolved values for (default: Infinity, i.e. cache forever).
  • maxErrorAge — an amount of milliseconds it should cache rejected values for (default: 0, i.e. don't cache).
  • resolve — serialiser to build unique key from fn arguments. (default: simple). Possible values:
    • simple (string) — convert each param to string & join those.
    • json (string) — JSON.stringify each param & join results.
    • function(Array) — custom function, with fn params as array on input
    • [ String, Boolean, 'json', function ] — array with custom functions, specific for each fn param position (text shortcuts as above are allowed).

Return value is a function with the same signature as fn.

Note. How prefetch works.

If maxAge used and request to cached data happens after 0.7 * maxAge time, then:

• cached data returned
• fn call is executed in parallel
• cached data will be substituted with new one on success, timeouts will be extended.

So your application will not have to wait for data fetch after cache expire.

memoizedFn(params...) -> promise

Returns result as cached promise (errors are not cached by default). If maxAge used, tries to prefetch new value before expire to replace cache transparently.

memoizedFn.clear()

Remove all cached data.

License

MIT