31Implement memoize() with custom cache keys

Implement memoize(fn, resolver). It returns a function that caches the results of fn, so calling it again with the same key returns the cached result without calling fn.

The cache key is:

• resolver(...args) when a resolver is given (called with the same this),
• otherwise the argument itself when there is exactly one argument,
• otherwise JSON.stringify(args).

The memoized function exposes its cache as memoized.cache (a Map), so callers can clear or inspect it.

const slowSquare = (n) => { /* expensive */ return n * n; };
const square = memoize(slowSquare);
square(9); // computed
square(9); // from the cache

const getUser = memoize(fetchUserProfile, (user) => user.id);
getUser({ id: 1, name: "A" });
getUser({ id: 1, name: "A (new object)" }); // cache hit: same id

Requirements

• Cache results that are undefined, null, 0 or false too.
• Objects passed as the only argument are compared by reference by default.
• Forward this to both fn and resolver.