https://github.com/nodeca/promise-memoize

Memoize promise-returning functions. Includes cache expire and prefetch.
https://github.com/nodeca/promise-memoize

Last synced: 1 day ago
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Memoize promise-returning functions. Includes cache expire and prefetch.

• Host: GitHub
• URL: https://github.com/nodeca/promise-memoize
• Owner: nodeca
• License: mit
• Created: 2016-05-20T15:41:20.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2018-12-05T12:15:57.000Z (about 6 years ago)
• Last Synced: 2024-04-14T04:22:26.953Z (9 months ago)
• Language: JavaScript
• Homepage:
• Size: 19.5 KB
• Stars: 58
• Watchers: 5
• Forks: 7
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

        
# promise-memoize

[![Build Status](https://img.shields.io/travis/nodeca/promise-memoize/master.svg?style=flat)](https://travis-ci.org/nodeca/promise-memoize)

[![NPM version](https://img.shields.io/npm/v/promise-memoize.svg?style=flat)](https://www.npmjs.org/package/promise-memoize)

[![Coverage Status](https://coveralls.io/repos/github/nodeca/promise-memoize/badge.svg?branch=master)](https://coveralls.io/github/nodeca/promise-memoize?branch=master)

> 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](https://developer.mozilla.org/docs/Web/API/WindowTimers/setTimeout)

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

### 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](https://github.com/nodeca/promise-memoize/blob/master/LICENSE)