useAsync in React
React interview exercise on Custom hooks, difficulty 3 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Write useAsync(fn, key): runs fn(key) when the key changes and returns { status, data, error, reload }: status "loading" | "success" | "error", data on success, error (the message) on failure, and reload() runs it again for the same key. An answer from a run that is no longer current must be ignored.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.