151. Async Memoization

Implement an async memoization utility that caches resolved results while safely managing in-flight concurrency to avoid duplicate work.

Unlike synchronous memoization, asynchronous requests introduce complex concurrency states. If multiple calls with the exact same arguments are made before the first request settles, only one underlying request should be made to prevent duplicated network/IO operations (request deduplication).

• In-Flight Deduplication: Concurrent requests with identical arguments must share the same Promise until settled.
• Success Caching: When a promise resolves, its result becomes permanently cached. Subsequent calls return the cached value directly.
• Failure Recovery: Rejected promises must not be cached. If an in-flight request fails, the cache entry must be cleared so the next consumer can trigger a fresh execution.
• Key Generation: Use JSON.stringify(args) to generate cache keys for strict argument matching.

Examples

const memoized = memoizeAsync(async (id) => {
  const res = await fetch(`/api/user/${id}`);
  return res.json();
});

// These three calls trigger only ONE network request
const [u1, u2, u3] = await Promise.all([
  memoized(101),
  memoized(101),
  memoized(101)
]);

// Subsequent calls return the cached user object immediately
const u4 = await memoized(101);