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

``bash
npm install promise-memoize --save
`

(\*) IE9 and below will require setTimeout polyfill
for correct work.

Usage example

`js
// 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('promise-memoize')(lastPosts, { maxAge: 60000 });

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

API

$3

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.

$3

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.

$3

Remove all cached data.

License

MIT