A developer on DEV Community tackled the challenge of limiting concurrent HTTP requests to six using JavaScript. Initial attempts with Promise.any failed because all requests acquired locks simultaneously due to microtask queue behavior. The solution evolved through multiple iterations.

A counter-based lock prevented queue overflow but still allowed race conditions. The final approach used a semaphore pattern with an explicit queue. Tasks exceeding the limit wait until a slot opens.Semaphore.acquire() holds new requests while Semaphore.release() triggers the next queued task.

The refactored class-based design wraps this logic cleanly. When tested with eight example tasks, only six ran immediately while two waited as intended. This matters for real-world applications that must respect API rate limits or avoid overwhelming servers.

JavaScript's single-threaded event loop makes such concurrency control tricky without proper queuing.