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Request scoping ​

Problem ​

You need an event bus scoped to a single HTTP request or user action. Listeners from one request must not bleed into the next, and all subscriptions should be released when the request completes.

Solution ​

Scope a bus to a single request and dispose it on cleanup:

ts
async function handleRequest(req: Request): Promise<Response> {
  using requestBus = createBus<RequestEvents>();

  requestBus.on('data:loaded', (data) => cache.set(req.url, data));

  await processRequest(req, requestBus);

  return buildResponse();
} // requestBus.dispose() called automatically

Pitfalls ​

  • Reusing one bus and calling removeAllListeners() between requests is not safe — it can remove listeners registered by a concurrent request. Create a new bus per request instead.
  • Not calling dispose() at the end of the request handler leaks the bus. Ensure disposal runs in a finally block so it fires even when the handler throws.
  • Passing the scoped bus through function arguments is safer than storing it on a shared object where concurrent requests can accidentally share a reference.