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* Events allow for applications to use the observer pattern, which
* allows subscribing and publishing events, outside the normal
* execution paths.
*
* @_section api/utils/events:Events [about-events]
*/
import { defineProperties } from "./properties.js";
/**
* A callback function called when a an event is triggered.
*/
export type Listener = (...args: Array<any>) => void;
/**
* An **EventEmitterable** behaves similar to an EventEmitter
* except provides async access to its methods.
*
* An EventEmitter implements the observer pattern.
*/
export interface EventEmitterable<T> {
/**
* Registers a %%listener%% that is called whenever the
* %%event%% occurs until unregistered.
*/
on(event: T, listener: Listener): Promise<this>;
/**
* Registers a %%listener%% that is called the next time
* %%event%% occurs.
*/
once(event: T, listener: Listener): Promise<this>;
/**
* Triggers each listener for %%event%% with the %%args%%.
*/
emit(event: T, ...args: Array<any>): Promise<boolean>;
/**
* Resolves to the number of listeners for %%event%%.
*/
listenerCount(event?: T): Promise<number>;
/**
* Resolves to the listeners for %%event%%.
*/
listeners(event?: T): Promise<Array<Listener>>;
/**
* Unregister the %%listener%% for %%event%%. If %%listener%%
* is unspecified, all listeners are unregistered.
*/
off(event: T, listener?: Listener): Promise<this>;
/**
* Unregister all listeners for %%event%%.
*/
removeAllListeners(event?: T): Promise<this>;
/**
* Alias for [[on]].
*/
addListener(event: T, listener: Listener): Promise<this>;
/**
* Alias for [[off]].
*/
removeListener(event: T, listener: Listener): Promise<this>;
}
/**
* When an [[EventEmitterable]] triggers a [[Listener]], the
* callback always ahas one additional argument passed, which is
* an **EventPayload**.
*/
export class EventPayload<T> {
/**
* The event filter.
*/
readonly filter!: T;
/**
* The **EventEmitterable**.
*/
readonly emitter!: EventEmitterable<T>;
readonly #listener: null | Listener;
/**
* Create a new **EventPayload** for %%emitter%% with
* the %%listener%% and for %%filter%%.
*/
constructor(emitter: EventEmitterable<T>, listener: null | Listener, filter: T) {
this.#listener = listener;
defineProperties<EventPayload<any>>(this, { emitter, filter });
}
/**
* Unregister the triggered listener for future events.
*/
async removeListener(): Promise<void> {
if (this.#listener == null) { return; }
await this.emitter.off(this.filter, this.#listener);
}
}
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