Review generated code that is subtly wrong

Medium30 minFree, no account

Clean, confident, well-commented, and broken in three places.

The question

A model produced the code below for "cache the result of an async function, deduplicating concurrent calls for the same key".

Find everything wrong with it. State how you would prove each one.

Generated. Looks fine.

const cache = new Map();

export function memoizeAsync(fn, ttlMs = 60_000) {
  return async function (key) {
    const hit = cache.get(key);
    if (hit && Date.now() - hit.at < ttlMs) {
      return hit.value;
    }

    const value = await fn(key);
    cache.set(key, { value, at: Date.now() });
    return value;
  };
}

30:00Commit to an answer before you open the solution. Reading it first teaches you to recognise good answers, which is not the skill being tested.

Stuck?

0 of 3 hints taken

The worked solution

written by a person · not a grade

Score yourself

0 of 5 marked

Found that concurrent deduplication is entirely absent35
Found the shared module-level cache15
Found the error-path and unbounded-growth problems20
Proposed storing the in-flight promise20
Proved each defect by running something, not by re-prompting10

We run no AI here and nothing on this page grades you. The score is yours, and the useful number is the one you get on the same problem a month from now, cold.

kept in this browser only