Notifier#

Subscription utility used internally by State and AttributeList.

Methods#

addListener(event, listener)#

Registers a listener for an event. Returns a release function to unsubscribe.

const release = notifier.addListener("change", (value) => {
  console.log(value)
})

// Unsubscribe
release()

If the listener has an onSubscribe callback, it is called immediately with the release function — useful for auto-cleanup:

const listener = (value: string) => console.log(value)

listener.onSubscribe = (release) => {
  node.addHook("BeforeRemove", release)  // auto-cleanup on node remove
}

notifier.addListener("change", listener)

removeListener(event, listener)#

Removes a specific listener from an event.

notifier.removeListener("change", listener)

notify(event, ...args)#

Calls all listeners registered for an event.

notifier.notify("change", newValue)

listenerCount(event)#

Returns the number of listeners subscribed to an event. Used internally by computed to stay lazy — an unobserved computed only marks itself dirty on a dependency change and defers recomputation until the next read.

const count = notifier.listenerCount("change") // e.g. 3

Handler type#

type Handler = ((...args: any[]) => any) & {
  onSubscribe?: (release: () => void) => void
}

onSubscribe is called once when the listener is registered. Use it to tie the listener's lifetime to another object.