mem

mem

Memoize functions - An optimization used to speed up consecutive function calls by caching the result of calls with identical input

Memory is automatically released when an item expires or the cache is cleared.

By default, only the first argument is considered and it only works with primitives. If you need to cache multiple arguments or cache objects by value, use the cacheKey option.

Install

$ npm install mem

Usage

const mem = require('mem');

let i = 0;
const counter = () => ++i;
const memoized = mem(counter);

memoized('foo');
//=> 1

// Cached as it's the same argument
memoized('foo');
//=> 1

// Not cached anymore as the argument changed
memoized('bar');
//=> 2

memoized('bar');
//=> 2

// Only the first argument is considered by default
memoized('bar', 'foo');
//=> 2

Works fine with promise returning functions

const mem = require('mem');

let i = 0;
const counter = async () => ++i;
const memoized = mem(counter);

(async () => {
	console.log(await memoized());
	//=> 1

	// The return value didn't increase as it's cached
	console.log(await memoized());
	//=> 1
})();

const mem = require('mem');
const got = require('got');
const delay = require('delay');

const memGot = mem(got, {maxAge: 1000});

(async () => {
	await memGot('sindresorhus.com');

	// This call is cached
	await memGot('sindresorhus.com');

	await delay(2000);

	// This call is not cached as the cache has expired
	await memGot('sindresorhus.com');
})();

API

mem(fn, options?)

fn

Type: Function

Function to be memoized.

options

Type: object

maxAge

Type: number
Default: Infinity

Milliseconds until the cache expires.

cacheKey

Type: Function
Default: arguments_ => arguments_[0]
Example: arguments_ => JSON.stringify(arguments_)

Determines the cache key for storing the result based on the function arguments. By default, only the first argument is considered.

A cacheKey function can return any type supported by Map (or whatever structure you use in the cache option).

You can have it cache all the arguments by value with JSON.stringify, if they are compatible:

const mem = require('mem');

mem(function_, {cacheKey: JSON.stringify});

Or you can use a more full-featured serializer like serialize-javascript to add support for RegExp, Date and so on.

const mem = require('mem');
const serializeJavascript = require('serialize-javascript');

mem(function_, {cacheKey: serializeJavascript});

cache

Type: object
Default: new Map()

Use a different cache storage. Must implement the following methods: .has(key), .get(key), .set(key, value), .delete(key), and optionally .clear(). You could for example use a WeakMap instead or quick-lru for a LRU cache.

mem.clear(fn)

Clear all cached data of a memoized function.

fn

Type: Function

Memoized function.

Tips

Cache statistics

If you want to know how many times your cache had a hit or a miss, you can make use of stats-map as a replacement for the default cache.

Example

const mem = require('mem');
const StatsMap = require('stats-map');
const got = require('got');

const cache = new StatsMap();
const memGot = mem(got, {cache});

(async () => {
	await memGot('sindresorhus.com');
	await memGot('sindresorhus.com');
	await memGot('sindresorhus.com');

	console.log(cache.stats);
	//=> {hits: 2, misses: 1}
})();

Related

• p-memoize - Memoize promise-returning & async functions

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