class ObservableObjectmethod

listenOnce()

Returns a promise for a single event with the provided name.

listenOnce(
  name: string,
  signal?: AbortSignal,
): Promise<ObservableEvent<this>>;

Parameters

• name — The name of the event
• signal — An optional AbortSignal that can be used to cancel the listener (or a polyfill)

Return value

A promise that resolves with the first matching event

Description

This method adds a listener for a single event with the specified name. When the event is emitted, the listener is removed and the returned promise resolves with the event.

The promise rejects with an error with name set to AbortError if:

• The provided signal is already aborted, or becomes aborted
• The object is unlinked before the event is emitted

Examples

// Wait for a single event
let event = await someObject.listenOnce("Loaded");

// Cancel using an abort signal (e.g. in afterActive)
async afterActive(signal: AbortSignal) {
  let event = await someObject.listenOnce("Loaded", signal);
  // ... (not reached if deactivated before event)
}

Related

• class ObservableObject
  The base class of all observable objects, which can be placed into a tree structure to enable event handling and data binding.
• listen()
  Adds a handler for all events emitted by this object.
• listenAsync()
  Adds a handler for all events emitted by this object, and returns an async iterable.