3.3 KiB
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.
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 arguments
memoized('foo');
//=> 1
// Not cached anymore as the arguments changed
memoized('bar');
//=> 2
memoized('bar');
//=> 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
Determines the cache key for storing the result based on the function arguments. By default, if there's only one argument and it's a primitive, it's used directly as a key, otherwise it's all the function arguments JSON stringified as an array.
You could for example change it to only cache on the first argument x => JSON.stringify(x).
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.
cachePromiseRejection
Type: boolean
Default: false
Cache rejected promises.
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
License
MIT © Sindre Sorhus