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Awaiting a one-time event ​

Problem ​

You need to wait for a single event to fire before continuing — without polling, without a callback, and without coupling the waiting code to the emitting code directly.

Solution ​

Use wait() for async coordination between modules:

ts
// Module A: waits for auth before doing work
async function loadDashboard() {
  const { userId } = await appBus.wait('user:login', AbortSignal.timeout(10_000));
  const data = await fetchDashboard(userId);
  renderDashboard(data);
}

// Module B: triggers the event independently
function onAuthSuccess(user: User) {
  appBus.emit('user:login', { userId: user.id, email: user.email });
}

Pitfalls ​

  • If the event fires before wait() is called, wait() hangs forever — there is no replay buffer. Ensure the emitter always fires after the listener is registered.
  • Calling wait() in a loop without awaiting creates multiple concurrent pending waits that all resolve with the same first emission. Await each one sequentially.
  • If the bus is disposed before the event fires, wait() rejects with BusDisposedError. Always handle this rejection in async code that awaits events on a scoped bus.