Clean up EventEmitter

Summary: As suggested by yungsters in D13138187

Reviewed By: mjesun

Differential Revision: D13192765

fbshipit-source-id: 8ab3dc74b3a9aaebf043bc3b5ed4f2590f480d10

Libraries/vendor/emitter/EventEmitter.js

@@ -16,8 +16,6 @@ const EventSubscriptionVendor = require('EventSubscriptionVendor');
 
 const invariant = require('fbjs/lib/invariant');
 
-const emptyFunctionThatReturnsTrue = () => true;
-
 /**
  * @class EventEmitter
  * @description
@@ -151,13 +149,9 @@ class EventEmitter {
    * @returns {array}
    */
   listeners(eventType: string): [EmitterSubscription] {
-    const subscriptions: ?[
-      EmitterSubscription,
-    ] = (this._subscriber.getSubscriptionsForType(eventType): any);
+    const subscriptions = this._subscriber.getSubscriptionsForType(eventType);
     return subscriptions
-      ? subscriptions
-          .filter(emptyFunctionThatReturnsTrue)
-          .map(subscription => subscription.listener)
+      ? subscriptions.map(subscription => subscription.listener)
       : [];
   }
 
@@ -176,9 +170,7 @@ class EventEmitter {
    *   emitter.emit('someEvent', 'abc'); // logs 'abc'
    */
   emit(eventType: string) {
-    const subscriptions: ?[
-      EmitterSubscription,
-    ] = (this._subscriber.getSubscriptionsForType(eventType): any);
+    const subscriptions = this._subscriber.getSubscriptionsForType(eventType);
     if (subscriptions) {
       for (let i = 0, l = subscriptions.length; i < l; i++) {
         const subscription = subscriptions[i];
@@ -210,9 +202,7 @@ class EventEmitter {
    *
    */
   removeListener(eventType: String, listener) {
-    const subscriptions: ?[
-      EmitterSubscription,
-    ] = (this._subscriber.getSubscriptionsForType(eventType): any);
+    const subscriptions = this._subscriber.getSubscriptionsForType(eventType);
     if (subscriptions) {
       for (let i = 0, l = subscriptions.length; i < l; i++) {
         const subscription = subscriptions[i];