Memoize promise-returning & async functions
npm install p-memoize> 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 memoize but with async-specific enhancements; in particular, it allows for asynchronous caches and does not cache rejected promises.
``sh`
npm install p-memoize
`js
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');
`
Similar to the caching strategy for memoize with the following exceptions:
- Promises returned from a memoized function are locally cached until resolving, when their value is added to cache. Special properties assigned to a returned promise will not be kept after resolution and every promise may need to resolve with a serializable object if caching results in a database..get()
- , .has() and .set() methods on cache can run asynchronously by returning a promise..set()
- Instead of 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.
Returns a memoized version of the given function.
#### fn
Type: Function
Promise-returning or async function to be memoized.
#### options
Type: object
##### cacheKey
Type: Function\arguments_ => arguments_[0]
Default: \arguments_ => JSON.stringify(arguments_)
Example:
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.
##### cache
Type: object | false\new Map()
Default:
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. To disable caching so that only concurrent executions resolve with the same value, pass false.
See the caching strategy section in the mem package for more information.
##### shouldCache
Type: (value, {key, argumentsList}) => boolean | Promise
Controls whether a fulfilled value should be written to the cache.
It runs after the function fulfills and before cache.set.
- Omit to keep current behavior (always write).
- Return false to skip writing to the cache (in-flight de-duplication is still cleared).
- Throw or reject to propagate the error and skip caching.
`js
import pMemoize from 'p-memoize';
// Only cache defined values
const getMaybe = pMemoize(async key => db.get(key), {
shouldCache: value => value !== undefined,
});
// Only cache non-empty arrays
const search = pMemoize(async query => fetchResults(query), {
shouldCache: value => Array.isArray(value) && value.length > 0,
});
`
Note: Affects only writes; reads from the cache are unchanged.
Returns a decorator to memoize class methods (instance and static).
Notes:
- Only class methods are supported; regular functions are not part of the decorators proposals.
- Requires the new ECMAScript decorators (TypeScript 5.0+). Legacy experimentalDecorators are not supported.
- Babel’s legacy decorators are not supported as they implement a different proposal variant.
- Private methods are not supported.
#### options
Type: object
Same as options for pMemoize().
`ts
import {pMemoizeDecorator} from 'p-memoize';
class Example {
index = 0
@pMemoizeDecorator()
async counter() {
return ++this.index;
}
}
class ExampleWithOptions {
index = 0
@pMemoizeDecorator()
async counter() {
return ++this.index;
}
}
`
The decorator memoizes per-instance. You can clear the cache for an instance method using pMemoizeClear(instance.method).
Clear all cached data of a memoized function.
It will throw when given a non-memoized function.
`js
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});
`
`js
import pMemoize from 'p-memoize';
import pReflect from 'p-reflect';
const memoizedGot = pMemoize(async (url, options) => pReflect(got(url, options)));
await memoizedGot('https://example.com');
// {isFulfilled: true, isRejected: false, value: '...'}
``
- p-debounce - Debounce promise-returning & async functions
- p-throttle - Throttle promise-returning & async functions
- More…