Hallucination drill: event-loop

event-loopFree sample

A team saw event-loop stalls while parsing large webhook payloads and asked an assistant to make the parse non-blocking. The assistant produced this wrapper and claimed that because the work now runs inside a promise, parsing happens off the main thread and requests keep flowing while it completes.

function parseAsync(json) {
  return new Promise((resolve, reject) => {
    try {
      resolve(JSON.parse(json));
    } catch (err) {
      reject(err);
    }
  });
}

Which one is the flaw?resolve() runs inside a try block and resolves with undefined, so callers receive no parsed data.A promise controls when the result is delivered. It does not move where the work runs. The executor runs synchronously on the calling thread, so JSON.parse blocks the event loop for exactly as long as it did before.Nothing is wrong. Promise executors are dispatched to the libuv threadpool, the same mechanism that makes fs.promises non-blocking.JSON.parse inside an executor throws ERR_SYNC_IN_ASYNC_CONTEXT in strict mode; the wrapper needs queueMicrotask instead.