Inlined DevTools event emitter

DevTools previously used the NPM events package for dispatching events. This package has an unfortunate flaw though- if a listener throws during event dispatch, no subsequent listeners are called. I've replaced that event dispatcher with my own implementation that ensures all listeners are called before it re-throws an error.

This commit replaces that event emitter with a custom implementation that calls all listeners before re-throwing an error.

packages/react-devtools-shared/package.json

@@ -11,7 +11,6 @@
     "@reach/menu-button": "^0.1.17",
     "@reach/tooltip": "^0.2.2",
     "clipboard-js": "^0.3.6",
-    "events": "^3.0.0",
     "local-storage-fallback": "^4.1.1",
     "lodash.throttle": "^4.1.1",
     "memoize-one": "^3.1.1",

packages/react-devtools-shared/src/backend/agent.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import EventEmitter from 'events';
+import EventEmitter from '../events';
 import throttle from 'lodash.throttle';
 import {
   SESSION_STORAGE_LAST_SELECTION_KEY,

packages/react-devtools-shared/src/bridge.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import EventEmitter from 'events';
+import EventEmitter from './events';
 
 import type {ComponentFilter, Wall} from './types';
 import type {

packages/react-devtools-shared/src/devtools/ProfilerStore.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import EventEmitter from 'events';
+import EventEmitter from '../events';
 import {prepareProfilingDataFrontendFromBackendAndStore} from './views/Profiler/utils';
 import ProfilingCache from './ProfilingCache';
 import Store from './store';

packages/react-devtools-shared/src/devtools/store.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import EventEmitter from 'events';
+import EventEmitter from '../events';
 import {inspect} from 'util';
 import {
   TREE_OPERATION_ADD,

packages/react-devtools-shared/src/events.js

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+export default class EventEmitter<Events: Object> {
+  listenersMap: Map<string, Set<Function>> = new Map();
+
+  addListener<Event: $Keys<Events>>(
+    event: Event,
+    listener: (...$ElementType<Events, Event>) => any,
+  ): void {
+    let listeners = this.listenersMap.get(event);
+    if (listeners === undefined) {
+      listeners = new Set();
+
+      this.listenersMap.set(event, listeners);
+    }
+
+    listeners.add(listener);
+  }
+
+  emit<Event: $Keys<Events>>(
+    event: Event,
+    ...args: $ElementType<Events, Event>
+  ): void {
+    const listeners = this.listenersMap.get(event);
+    if (listeners !== undefined) {
+      let didThrow = false;
+      let caughtError = null;
+
+      listeners.forEach(listener => {
+        try {
+          listener.apply(null, args);
+        } catch (error) {
+          if (caughtError === null) {
+            didThrow = true;
+            caughtError = error;
+          }
+        }
+      });
+
+      if (didThrow) {
+        throw caughtError;
+      }
+    }
+  }
+
+  removeAllListeners(event?: $Keys<Events>): void {
+    if (event != null) {
+      this.listenersMap.delete(event);
+    } else {
+      this.listenersMap.clear();
+    }
+  }
+
+  removeListener(event: $Keys<Events>, listener: Function): void {
+    const listeners = this.listenersMap.get(event);
+    if (listeners !== undefined) {
+      listeners.delete(listener);
+    }
+  }
+}

scripts/flow/react-devtools.js

@@ -7,19 +7,4 @@
  * @flow
  */
 
-declare module 'events' {
-  declare class EventEmitter<Events: Object> {
-    addListener<Event: $Keys<Events>>(
-      event: Event,
-      listener: (...$ElementType<Events, Event>) => any,
-    ): void;
-    emit: <Event: $Keys<Events>>(
-      event: Event,
-      ...$ElementType<Events, Event>
-    ) => void;
-    removeListener(event: $Keys<Events>, listener: Function): void;
-    removeAllListeners(event?: $Keys<Events>): void;
-  }
-
-  declare export default typeof EventEmitter;
-}
+// No types