Function once

once<Payload extends unknown>(
    hub: Hub,
    channel: ChannelRoute,
    callback: Callback<Payload>,
    onlyFuture?: boolean,
): (reason?: string) => void
Run a callback once.
Type Parameters
- Payload extends unknown
Parameters
- hub: Hub
  The hub this listener should attach to.
- channel: ChannelRoute
  Name of the channel to subscribe to. Does not need to exist to be subscribed to. Passing * will subscribe to all channels.
- callback: Callback<Payload>
  Called with message payload and channel name when a message is published.
- OptionalonlyFuture: boolean = false
  If true, callback will fire only for messages dispatched in the future. If false, messages in the backlog will also be considered.
Returns (reason?: string) => void
Example
```
const hub = new Hub();

once(hub, 'sandwiches', (p) => console.log(`once: ${p}`));

hub.pub('sandwiches', 'reuben sandwich');
// "once: reuben sandwich"
hub.pub('sandwiches', 'chicken sandwich');
// Nothing printed.
```
- Defined in work/denden/denden/src/extensions/conditionals.ts:86