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    6.0.1 • Public • Published


    Memoize promise-returning & async functions

    Useful for speeding up consecutive function calls by caching the result of calls with identical input.

    By default, only the memoized function's first argument is considered via strict equality comparison. If you need to cache multiple arguments or cache objects by value, have a look at alternative caching strategies below.

    This package is similar to mem but with async-specific enhancements; in particular, it allows for asynchronous caches and does not cache rejected promises by default (unless the cachePromiseRejection option is set).


    $ npm install p-memoize


    import {setTimeout as delay} from 'node:timer/promises';
    import pMemoize from 'p-memoize';
    import got from 'got';
    const memoizedGot = pMemoize(got);
    await memoizedGot('https://sindresorhus.com');
    // This call is cached
    await memoizedGot('https://sindresorhus.com');
    await delay(2000);
    // This call is not cached as the cache has expired
    await memoizedGot('https://sindresorhus.com');

    Caching strategy

    Similar to the caching strategy for mem with the following exceptions:

    • Promises returned from a memoized function will be cached internally and take priority over cache if a value exists in both caches. The promise cache does not persist outside of the current instance and properties assigned to a returned promise will not be kept. All cached promises can be cleared with pMemoizeClear().
    • .get() and .has() methods on cache can return a promise instead of returning a value immediately.
    • Instead of .set() being provided an object with the properties value and maxAge, it will only be provided value as the first argument. If you want to implement time-based expiry, consider doing so in cache.


    pMemoize(fn, options?)

    Returns a memoized version of the given function.


    Type: Function

    Promise-returning or async function to be memoized.


    Type: object

    See the mem options in addition to the below option.


    Type: boolean
    Default: false

    Cache rejected promises.


    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).

    See the caching strategy section for more information.


    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.

    See the caching strategy section in the mem package for more information.


    Returns a decorator to memoize class methods or static class methods.


    • Only class methods and getters/setters can be memoized, not regular functions (they aren't part of the proposal);
    • Only TypeScript’s decorators are supported, not Babel’s, which use a different version of the proposal;
    • Being an experimental feature, they need to be enabled with --experimentalDecorators; follow TypeScript’s docs.


    Type: object

    Same as options for pMemoize().

    import {pMemoizeDecorator} from 'p-memoize';
    class Example {
    	index = 0
    	async counter() {
    		return ++this.index;
    class ExampleWithOptions {
    	index = 0
    	async counter() {
    		return ++this.index;


    Clear all cached data of a memoized function.

    It will throw when given a non-memoized function.


    Time-based cache expiration

    import pMemoize from 'p-memoize';
    import ExpiryMap from 'expiry-map';
    import got from 'got';
    const cache = new ExpiryMap(10000); // Cached values expire after 10 seconds
    const memoizedGot = pMemoize(got, {cache});



    npm i p-memoize

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    • sindresorhus
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