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Separate Package for @react-native/event-emitter 
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‎Libraries/vendor/emitter/EventEmitter.js

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* @format
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*/
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export interface EventSubscription {
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remove(): void;
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}
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export interface IEventEmitter<TEventToArgsMap: {...}> {
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addListener<TEvent: $Keys<TEventToArgsMap>>(
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eventType: TEvent,
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listener: (...args: $ElementType<TEventToArgsMap, TEvent>) => mixed,
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context?: mixed,
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): EventSubscription;
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emit<TEvent: $Keys<TEventToArgsMap>>(
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eventType: TEvent,
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...args: $ElementType<TEventToArgsMap, TEvent>
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): void;
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removeAllListeners<TEvent: $Keys<TEventToArgsMap>>(eventType?: ?TEvent): void;
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listenerCount<TEvent: $Keys<TEventToArgsMap>>(eventType: TEvent): number;
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}
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interface Registration<TArgs> {
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+context: mixed;
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+listener: (...args: TArgs) => mixed;
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+remove: () => void;
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}
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type Registry<TEventToArgsMap: {...}> = $ObjMap<
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TEventToArgsMap,
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<TArgs>(TArgs) => Set<Registration<TArgs>>,
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>;
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/**
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* EventEmitter manages listeners and publishes events to them.
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*
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* EventEmitter accepts a single type parameter that defines the valid events
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* and associated listener argument(s).
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*
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* @example
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*
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* const emitter = new EventEmitter<{
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* success: [number, string],
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* error: [Error],
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* }>();
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*
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* emitter.on('success', (statusCode, responseText) => {...});
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* emitter.emit('success', 200, '...');
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*
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* emitter.on('error', error => {...});
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* emitter.emit('error', new Error('Resource not found'));
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*
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*/
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export default class EventEmitter<TEventToArgsMap: {...}>
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implements IEventEmitter<TEventToArgsMap>
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{
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_registry: Registry<TEventToArgsMap> = {};
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/**
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* Registers a listener that is called when the supplied event is emitted.
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* Returns a subscription that has a `remove` method to undo registration.
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*/
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addListener<TEvent: $Keys<TEventToArgsMap>>(
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eventType: TEvent,
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listener: (...args: $ElementType<TEventToArgsMap, TEvent>) => mixed,
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context: mixed,
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): EventSubscription {
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const registrations = allocate(this._registry, eventType);
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const registration: Registration<$ElementType<TEventToArgsMap, TEvent>> = {
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context,
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listener,
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remove(): void {
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registrations.delete(registration);
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},
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};
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registrations.add(registration);
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return registration;
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}
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/**
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* Emits the supplied event. Additional arguments supplied to `emit` will be
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* passed through to each of the registered listeners.
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*
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* If a listener modifies the listeners registered for the same event, those
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* changes will not be reflected in the current invocation of `emit`.
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*/
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emit<TEvent: $Keys<TEventToArgsMap>>(
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eventType: TEvent,
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...args: $ElementType<TEventToArgsMap, TEvent>
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): void {
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const registrations: ?Set<
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Registration<$ElementType<TEventToArgsMap, TEvent>>,
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> = this._registry[eventType];
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if (registrations != null) {
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for (const registration of [...registrations]) {
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registration.listener.apply(registration.context, args);
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}
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}
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}
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/**
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* Removes all registered listeners.
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*/
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removeAllListeners<TEvent: $Keys<TEventToArgsMap>>(
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eventType?: ?TEvent,
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): void {
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if (eventType == null) {
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this._registry = {};
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} else {
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delete this._registry[eventType];
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}
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}
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/**
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* Returns the number of registered listeners for the supplied event.
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*/
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listenerCount<TEvent: $Keys<TEventToArgsMap>>(eventType: TEvent): number {
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const registrations: ?Set<Registration<mixed>> = this._registry[eventType];
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return registrations == null ? 0 : registrations.size;
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}
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}
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function allocate<
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TEventToArgsMap: {...},
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TEvent: $Keys<TEventToArgsMap>,
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TEventArgs: $ElementType<TEventToArgsMap, TEvent>,
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>(
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registry: Registry<TEventToArgsMap>,
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eventType: TEvent,
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): Set<Registration<TEventArgs>> {
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let registrations: ?Set<Registration<TEventArgs>> = registry[eventType];
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if (registrations == null) {
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registrations = new Set();
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registry[eventType] = registrations;
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}
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return registrations;
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}
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import type {
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EventSubscription,
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IEventEmitter,
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} from '@react-native/event-emitter';
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import EventEmitter from '@react-native/event-emitter';
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export type {EventSubscription, IEventEmitter};
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export default EventEmitter;

‎package.json

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"@react-native-community/cli-platform-android": "^9.0.0-alpha.10",
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"@react-native-community/cli-platform-ios": "^9.0.0-alpha.10",
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"@react-native/assets": "1.0.0",
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"@react-native/event-emitter": "^0.71.0",
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"@react-native/normalize-color": "2.0.0",
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"@react-native/polyfills": "2.0.0",
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"abort-controller": "^3.0.0",

‎packages/event-emitter/.babelrc

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{
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"presets": ["@babel/preset-flow"]
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}

‎packages/event-emitter/README.md

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# @react-native/event-emitter
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`@react-native/event-emitter` is an event library used by React Native that is
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published as an independent package so it can also be used by applications.
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Consult the included type definitions for usage instructions.
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## License
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`idx` is [MIT licensed](./LICENSE).

‎packages/event-emitter/lib/EventEmitter.d.ts

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/**
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*
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* @format
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*/
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export interface EventSubscription {
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remove(): void;
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}
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export interface IEventEmitter<TEventToArgsMap extends {[eventType: string]: unknown[]}> {
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addListener<TEvent extends keyof TEventToArgsMap>(
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eventType: TEvent,
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listener: (...args: TEventToArgsMap[TEvent]) => void,
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context?: unknown,
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): EventSubscription;
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emit<TEvent extends keyof TEventToArgsMap>(
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eventType: TEvent,
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...args: TEventToArgsMap[TEvent]
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): void;
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removeAllListeners<TEvent extends keyof TEventToArgsMap>(eventType?: TEvent | null): void;
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listenerCount<TEvent extends keyof TEventToArgsMap>(eventType: TEvent): number;
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}
30+
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/**
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* EventEmitter manages listeners and publishes events to them.
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*
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* EventEmitter accepts a single type parameter that defines the valid events
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* and associated listener argument(s).
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*
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* @example
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*
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* const emitter = new EventEmitter<{
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* success: [number, string],
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* error: [Error],
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* }>();
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*
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* emitter.on('success', (statusCode, responseText) => {...});
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* emitter.emit('success', 200, '...');
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*
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* emitter.on('error', error => {...});
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* emitter.emit('error', new Error('Resource not found'));
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*
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*/
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export default class EventEmitter<TEventToArgsMap extends {[eventType: string]: unknown[]}> implements IEventEmitter<TEventToArgsMap> {
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/**
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* Registers a listener that is called when the supplied event is emitted.
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* Returns a subscription that has a `remove` method to undo registration.
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*/
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addListener<TEvent extends keyof TEventToArgsMap>(
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eventType: TEvent,
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listener: (...args: TEventToArgsMap[TEvent]) => void,
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context?: unknown,
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): EventSubscription;
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/**
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* Emits the supplied event. Additional arguments supplied to `emit` will be
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* passed through to each of the registered listeners.
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*
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* If a listener modifies the listeners registered for the same event, those
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* changes will not be reflected in the current invocation of `emit`.
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*/
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emit<TEvent extends keyof TEventToArgsMap>(
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eventType: TEvent,
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...args: TEventToArgsMap[TEvent]
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): void;
73+
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/**
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* Removes all registered listeners.
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*/
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removeAllListeners<TEvent extends keyof TEventToArgsMap>(eventType?: TEvent | null): void;
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79+
/**
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* Returns the number of registered listeners for the supplied event.
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*/
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listenerCount<TEvent extends keyof TEventToArgsMap>(eventType: TEvent): number;
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}

‎packages/event-emitter/lib/EventEmitter.js

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/**
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
6+
*
7+
*
8+
* @format
9+
*/
10+
11+
/**
12+
* EventEmitter manages listeners and publishes events to them.
13+
*
14+
* EventEmitter accepts a single type parameter that defines the valid events
15+
* and associated listener argument(s).
16+
*
17+
* @example
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*
19+
* const emitter = new EventEmitter<{
20+
* success: [number, string],
21+
* error: [Error],
22+
* }>();
23+
*
24+
* emitter.on('success', (statusCode, responseText) => {...});
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* emitter.emit('success', 200, '...');
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*
27+
* emitter.on('error', error => {...});
28+
* emitter.emit('error', new Error('Resource not found'));
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*
30+
*/
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export default class EventEmitter {
32+
_registry = {};
33+
/**
34+
* Registers a listener that is called when the supplied event is emitted.
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* Returns a subscription that has a `remove` method to undo registration.
36+
*/
37+
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addListener(eventType, listener, context) {
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const registrations = allocate(this._registry, eventType);
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const registration = {
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context,
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listener,
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remove() {
45+
registrations.delete(registration);
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},
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};
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registrations.add(registration);
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return registration;
50+
}
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/**
52+
* Emits the supplied event. Additional arguments supplied to `emit` will be
53+
* passed through to each of the registered listeners.
54+
*
55+
* If a listener modifies the listeners registered for the same event, those
56+
* changes will not be reflected in the current invocation of `emit`.
57+
*/
58+
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emit(eventType, ...args) {
60+
const registrations = this._registry[eventType];
61+
62+
if (registrations != null) {
63+
for (const registration of [...registrations]) {
64+
registration.listener.apply(registration.context, args);
65+
}
66+
}
67+
}
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/**
69+
* Removes all registered listeners.
70+
*/
71+
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removeAllListeners(eventType) {
73+
if (eventType == null) {
74+
this._registry = {};
75+
} else {
76+
delete this._registry[eventType];
77+
}
78+
}
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/**
80+
* Returns the number of registered listeners for the supplied event.
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*/
82+
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listenerCount(eventType) {
84+
const registrations = this._registry[eventType];
85+
return registrations == null ? 0 : registrations.size;
86+
}
87+
}
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function allocate(registry, eventType) {
90+
let registrations = registry[eventType];
91+
92+
if (registrations == null) {
93+
registrations = new Set();
94+
registry[eventType] = registrations;
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}
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return registrations;
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}

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