Consume Ongoing Events

Problem

A component or service needs every future event until its owner ends.

Solution

Use on() with an ownership signal. Herald delivers synchronously and keeps no queue.

const controller = new AbortController();

appBus.on(
  'cart:updated',
  ({ items, total }) => {
    renderCart(items, total);
  },
  { signal: controller.signal },
);

controller.abort();

Use wait() when only the next event matters:

const cart = await appBus.wait('cart:updated', {
  signal: AbortSignal.timeout(30_000),
});

Pitfalls

• Events emitted before registration are not replayed.
• Herald does not buffer or provide backpressure. Use a dedicated queue or stream when asynchronous sequential consumption is required.
• Listener callbacks run inside emit(). Keep them short and handle asynchronous failures explicitly.
• Aborting the ownership signal removes the subscription but does not dispose the bus.

Related

• Awaiting a one-time event
• Usage Guide