Function once

once<K>(evt, fn): Unsubscribe
Subscribe to an event for a single delivery, then auto-unsubscribe.
Type Parameters
- K extends keyof EventMap
Parameters
- evt: K
  
  The event name (a key of EventMap).
- fn: ((payload) => void)
  
  Handler that receives the event payload once.
  - - (payload): void
    - Parameters
      
      payload: EventMap[K]
      
      Returns void
Returns Unsubscribe
A function that cancels the subscription before it fires.
- Defined in packages/core/subpaths/events/index.ts:46