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