[skip ci] Add benchmark for EventTarget (facebook#48886)

Summary:

Changelog: [internal]

Creates a benchmarks to measure the performance of `EventTarget`.

Differential Revision: D67750677

packages/react-native/src/private/webapis/dom/events/__tests__/EventTarget-benchmark-itest.js

@@ -0,0 +1,110 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import '../../../../../../Libraries/Core/InitializeCore.js';
+
+import Event from '../Event';
+import EventTarget from '../EventTarget';
+import createEventTargetHierarchyWithDepth from './createEventTargetHierarchyWithDepth';
+import {unstable_benchmark} from '@react-native/fantom';
+
+let event: Event;
+let eventTarget: EventTarget;
+
+unstable_benchmark
+  .suite('EventTarget')
+  .add(
+    'dispatchEvent, no bubbling, no listeners',
+    () => {
+      eventTarget.dispatchEvent(event);
+    },
+    {
+      beforeAll: () => {
+        event = new Event('custom');
+        eventTarget = new EventTarget();
+      },
+    },
+  )
+  .add(
+    'dispatchEvent, no bubbling, single listener',
+    () => {
+      eventTarget.dispatchEvent(event);
+    },
+    {
+      beforeAll: () => {
+        event = new Event('custom');
+        eventTarget = new EventTarget();
+        eventTarget.addEventListener('custom', () => {});
+      },
+    },
+  )
+  .add(
+    'dispatchEvent, no bubbling, multiple listeners',
+    () => {
+      eventTarget.dispatchEvent(event);
+    },
+    {
+      beforeAll: () => {
+        event = new Event('custom');
+        eventTarget = new EventTarget();
+        for (let i = 0; i < 100; i++) {
+          eventTarget.addEventListener('custom', () => {});
+        }
+      },
+    },
+  )
+  .add(
+    'dispatchEvent, bubbling, no listeners',
+    () => {
+      eventTarget.dispatchEvent(event);
+    },
+    {
+      beforeAll: () => {
+        event = new Event('custom', {bubbles: true});
+        const targets = createEventTargetHierarchyWithDepth(100);
+        eventTarget = targets[targets.length - 1];
+      },
+    },
+  )
+  .add(
+    'dispatchEvent, bubbling, single listener per target',
+    () => {
+      eventTarget.dispatchEvent(event);
+    },
+    {
+      beforeAll: () => {
+        event = new Event('custom', {bubbles: true});
+        const targets = createEventTargetHierarchyWithDepth(100);
+        eventTarget = targets[targets.length - 1];
+        for (const target of targets) {
+          target.addEventListener('custom', () => {});
+        }
+      },
+    },
+  )
+  .add(
+    'dispatchEvent, bubbling, multiple listeners per target',
+    () => {
+      eventTarget.dispatchEvent(event);
+    },
+    {
+      beforeAll: () => {
+        event = new Event('custom', {bubbles: true});
+        const targets = createEventTargetHierarchyWithDepth(100);
+        eventTarget = targets[targets.length - 1];
+        for (const target of targets) {
+          for (let i = 0; i < 100; i++) {
+            target.addEventListener('custom', () => {});
+          }
+        }
+      },
+    },
+  );

packages/react-native/src/private/webapis/dom/events/__tests__/EventTarget-itest.js

@@ -14,10 +14,8 @@ import '../../../../../../Libraries/Core/InitializeCore.js';
 
 import Event from '../Event';
 import EventTarget from '../EventTarget';
-import {
-  EVENT_TARGET_GET_THE_PARENT_KEY,
-  dispatchTrustedEvent,
-} from '../internals/EventTargetInternals';
+import {dispatchTrustedEvent} from '../internals/EventTargetInternals';
+import createEventTargetHierarchyWithDepth from './createEventTargetHierarchyWithDepth';
 
 let listenerCallOrder = 0;
 
@@ -57,24 +55,6 @@ function createListener(
   return listener;
 }
 
-function createEventTargetHierarchyWithDepth(
-  depth: number,
-): Array<EventTarget> {
-  const targets = [];
-
-  for (let i = 0; i < depth; i++) {
-    const target = new EventTarget();
-    const parentTarget = targets[targets.length - 1];
-
-    // $FlowExpectedError[prop-missing]
-    target[EVENT_TARGET_GET_THE_PARENT_KEY] = () => parentTarget;
-
-    targets.push(target);
-  }
-
-  return targets;
-}
-
 describe('EventTarget', () => {
   describe('addEventListener', () => {
     it('should throw an error if event or callback are NOT passed', () => {

packages/react-native/src/private/webapis/dom/events/__tests__/createEventTargetHierarchyWithDepth.js

@@ -0,0 +1,38 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import EventTarget from '../EventTarget';
+import {EVENT_TARGET_GET_THE_PARENT_KEY} from '../internals/EventTargetInternals';
+
+/**
+ * Returns a tree of EventTargets with the given depth (starting from the root).
+ */
+export default function createEventTargetHierarchyWithDepth(
+  depth: number,
+): Array<EventTarget> {
+  if (depth < 1) {
+    throw new Error('Depth must be greater or equal to 1');
+  }
+
+  const targets = [];
+
+  for (let i = 0; i < depth; i++) {
+    const target = new EventTarget();
+    const parentTarget = targets[targets.length - 1];
+
+    // $FlowExpectedError[prop-missing]
+    target[EVENT_TARGET_GET_THE_PARENT_KEY] = () => parentTarget;
+
+    targets.push(target);
+  }
+
+  return targets;
+}