RN: Simplify RCTDeviceEventEmitter

Summary:
Simplifies `RCTDeviceEventEmitter` to simply be an `EventEmitter`.

The only thing special about it is that all native events are emitted on it and that `NativeEventEmitter` composes it.

Changelog:
[General][Removed] - Removed `RCTDeviceEventEmitter.sharedSubscribers`.

Reviewed By: RSNara

Differential Revision: D26163660

fbshipit-source-id: aedff8323d86947220fc293a74a19a3981fd875a

Author: yungsters

Libraries/EventEmitter/RCTDeviceEventEmitter.js

@@ -4,41 +4,19 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
+ * @flow strict
  * @format
- * @flow
  */
 
-import EventEmitter from '../vendor/emitter/EventEmitter';
-import type EmitterSubscription from '../vendor/emitter/_EmitterSubscription';
-import EventSubscriptionVendor from '../vendor/emitter/_EventSubscriptionVendor';
-
-/**
- * Deprecated - subclass NativeEventEmitter to create granular event modules instead of
- * adding all event listeners directly to RCTDeviceEventEmitter.
- */
-class RCTDeviceEventEmitter<
-  EventDefinitions: {...},
-> extends EventEmitter<EventDefinitions> {
-  sharedSubscriber: EventSubscriptionVendor<EventDefinitions>;
-
-  constructor() {
-    const sharedSubscriber = new EventSubscriptionVendor<EventDefinitions>();
-    super(sharedSubscriber);
-    this.sharedSubscriber = sharedSubscriber;
-  }
-
-  removeSubscription<K: $Keys<EventDefinitions>>(
-    subscription: EmitterSubscription<EventDefinitions, K>,
-  ): void {
-    if (subscription.emitter !== this) {
-      subscription.emitter.removeSubscription(subscription);
-    } else {
-      super.removeSubscription(subscription);
-    }
-  }
-}
+import EventEmitter, {type IEventEmitter} from '../vendor/emitter/EventEmitter';
 
 // FIXME: use typed events
 type RCTDeviceEventDefinitions = $FlowFixMe;
 
-export default (new RCTDeviceEventEmitter(): RCTDeviceEventEmitter<RCTDeviceEventDefinitions>);
+/**
+ * Global EventEmitter used by the native platform to emit events to JavaScript.
+ * Events are identified by globally unique event names.
+ *
+ * NativeModules that emit events should instead subclass `NativeEventEmitter`.
+ */
+export default (new EventEmitter(): IEventEmitter<RCTDeviceEventDefinitions>);

Libraries/EventEmitter/__mocks__/NativeEventEmitter.js

@@ -5,19 +5,42 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
-import EventEmitter from '../../vendor/emitter/EventEmitter';
+import {
+  type EventSubscription,
+  type IEventEmitter,
+} from '../../vendor/emitter/EventEmitter';
 import RCTDeviceEventEmitter from '../RCTDeviceEventEmitter';
 
 /**
- * Mock the NativeEventEmitter as a normal JS EventEmitter.
+ * Mock `NativeEventEmitter` to ignore Native Modules.
  */
-export default class NativeEventEmitter<
-  EventDefinitions: {...},
-> extends EventEmitter<EventDefinitions> {
-  constructor() {
-    super(RCTDeviceEventEmitter.sharedSubscriber);
+export default class NativeEventEmitter<TEventToArgsMap: {...}>
+  implements IEventEmitter<TEventToArgsMap> {
+  addListener<TEvent: $Keys<TEventToArgsMap>>(
+    eventType: TEvent,
+    listener: (...args: $ElementType<TEventToArgsMap, TEvent>) => mixed,
+    context?: mixed,
+  ): EventSubscription {
+    return RCTDeviceEventEmitter.addListener(eventType, listener, context);
+  }
+
+  emit<TEvent: $Keys<TEventToArgsMap>>(
+    eventType: TEvent,
+    ...args: $ElementType<TEventToArgsMap, TEvent>
+  ): void {
+    RCTDeviceEventEmitter.emit(eventType, ...args);
+  }
+
+  removeAllListeners<TEvent: $Keys<TEventToArgsMap>>(
+    eventType?: ?TEvent,
+  ): void {
+    RCTDeviceEventEmitter.removeAllListeners(eventType);
+  }
+
+  listenerCount<TEvent: $Keys<TEventToArgsMap>>(eventType: TEvent): number {
+    return RCTDeviceEventEmitter.listenerCount(eventType);
   }
 }

Libraries/vendor/emitter/EventEmitter.js

@@ -28,7 +28,7 @@ export interface IEventEmitter<TEventToArgsMap: {...}> {
    */
   addListener<TEvent: $Keys<TEventToArgsMap>>(
     eventType: TEvent,
-    listener: (...args: $ElementType<TEventToArgsMap, TEvent>) => void,
+    listener: (...args: $ElementType<TEventToArgsMap, TEvent>) => mixed,
     context?: mixed,
   ): EventSubscription;