Function memoizePromise

Create a Promise-returning Function that returns the memoized results of a Promise. The key for the lookup cache is determined by the keyExtractor Function.

An optional Map instance can be provided to be used as cache. This allows for example to prepopulate the cache, or to force recomputation of some values by removing their corresponding keys. If no instance is provided an empty Map will be created.

Remarks

If the Promise throws an error, no result will be cached and the Promise will be run again next time.

Example

Memoize the fetch function

const keyExtractor = (url) => url;

const memoizedFetch = memoizePromise(fetch, keyExtractor);

const result1 = memoizedFetch("https://...");
const result2 = memoizedFetch("https://...");
// fetch will only be called once

Example

Provide an initial cache restored from database

const restoredCacheFromDatabase = new Map([["https://...", 1]]);

const keyExtractor = (url) => url;

const memoizedFetch = memoizePromise(fetch, keyExtractor, restoredCacheFromDatabase);

const result = memoizedFetch("https://...");
// result will be directly returned from cache

Example

Clear cache after 5 seconds

const cache = new Map();
const keyExtractor = (url) => url;

const memoizedFetch = memoizePromise(fetch, keyExtractor, cache);

// ... fill the cache

setTimeout(() => {
  cache.clear();
}, 5000);

Returns

the memoized result