Creates a bus with no subscribers yet, and a publisher on it.
Optionalcapacity: number | null
how many events a slow subscriber may fall behind before it starts missing them, rounded up to the next power of two and at most 1048576; 64 when not given.
Hands an event to every current subscriber: bytes, or text such as an event name.
It never waits.
How many subscribers the event was handed to; an event published while no one is subscribed is dropped, and this is 0.
Takes another publisher on the same bus, for another part that announces.
A publish-only handle to an event bus.
It has no queue of its own, so a part that only announces never fills a buffer it does not read, and publishing from it returns how many subscribers the event was handed to.