From e7a4dbcefc9e393c41f4a796d522211bc1e60b6f Mon Sep 17 00:00:00 2001
From: Pieter Vanderwerff <pieterv@fb.com>
Date: Wed, 22 Jun 2022 21:36:52 -0700
Subject: [PATCH] Add LTI annotations to function params in xplat/js [1/2]

Summary: Add annotations to function parameters required for Flow's Local Type Inference project. This codemod prepares the codebase to match Flow's new typechecking algorithm. The new algorithm will make Flow more reliable and predicatable.

Reviewed By: evanyeung

Differential Revision: D37353648

fbshipit-source-id: e5a0c685ced85a8ff353d578b373f836b376bb28
---
 IntegrationTests/AsyncStorageTest.js          | 22 +++++-
 Libraries/Alert/Alert.js                      |  2 +-
 Libraries/Animated/AnimatedEvent.js           | 11 +--
 Libraries/Animated/AnimatedImplementation.js  |  6 +-
 Libraries/Animated/AnimatedMock.js            |  4 +-
 Libraries/Animated/nodes/AnimatedColor.js     |  2 +-
 Libraries/Animated/nodes/AnimatedValueXY.js   |  2 +-
 Libraries/BatchedBridge/MessageQueue.js       |  4 +-
 Libraries/Components/ScrollView/ScrollView.js |  6 +-
 Libraries/Components/Touchable/PooledClass.js |  8 +--
 Libraries/Components/Touchable/Touchable.js   | 13 +++-
 .../Touchable/TouchableNativeFeedback.js      |  4 +-
 Libraries/Core/Timers/JSTimers.js             |  4 +-
 Libraries/Inspector/NetworkOverlay.js         |  9 ++-
 Libraries/Lists/ViewabilityHelper.js          | 10 ++-
 Libraries/Lists/VirtualizedList.js            | 17 +++--
 Libraries/Lists/VirtualizedSectionList.js     | 13 ++--
 Libraries/LogBox/Data/LogBoxData.js           |  2 +-
 .../LogBox/Data/__tests__/LogBoxLog-test.js   |  2 +-
 .../__tests__/LogBoxSymbolication-test.js     |  2 +-
 .../LogBox/UI/LogBoxInspectorStackFrames.js   | 11 ++-
 .../StaticViewConfigValidator-test.js         |  4 +-
 Libraries/Pressability/Pressability.js        | 23 +++++--
 .../__tests__/Pressability-test.js            |  4 +-
 Libraries/ReactNative/PaperUIManager.js       |  2 +-
 Libraries/Text/Text.js                        | 14 ++--
 Libraries/Utilities/HMRClient.js              |  6 +-
 Libraries/Utilities/ReactNativeTestTools.js   |  4 +-
 Libraries/Vibration/Vibration.js              |  2 +-
 .../androidTest/js/ScrollViewTestModule.js    | 15 ++--
 .../tools/msggen/src/HeaderWriter.js          |  2 +-
 .../inspector/tools/msggen/src/index.js       |  4 +-
 .../src/generators/RNCodegen.js               |  2 +-
 .../src/generators/components/CppHelpers.js   |  8 ++-
 .../components/GenerateEventEmitterCpp.js     | 15 +++-
 .../components/GenerateEventEmitterH.js       | 16 ++++-
 .../generators/components/GeneratePropsCpp.js |  2 +-
 .../generators/components/GeneratePropsH.js   | 68 ++++++++++++++++---
 .../components/GeneratePropsJavaDelegate.js   | 15 ++--
 .../components/GeneratePropsJavaInterface.js  | 11 +--
 .../generators/components/GenerateTests.js    |  8 ++-
 .../generators/modules/GenerateModuleCpp.js   |  2 +-
 .../src/generators/modules/GenerateModuleH.js |  2 +-
 .../src/parsers/flow/components/props.js      |  3 +-
 .../__tests__/module-parser-e2e-test.js       |  6 +-
 .../src/parsers/flow/modules/index.js         |  2 +-
 .../parsers/typescript/components/props.js    |  3 +-
 .../typescript-module-parser-e2e-test.js      |  6 +-
 .../src/parsers/typescript/modules/index.js   |  2 +-
 .../examples/AnimatedGratuitousApp/AnExApp.js |  4 +-
 .../js/examples/Button/ButtonExample.js       |  2 +-
 .../RNTesterPlatformTestResultView.js         |  3 +-
 .../PointerEventSupport.js                    | 13 ++--
 .../Experimental/W3CPointerEventsExample.js   |  5 +-
 .../FlatList/FlatList-onEndReached.js         |  3 +-
 .../FlatList/FlatList-withSeparators.js       |  9 ++-
 .../js/examples/Image/ImageExample.js         |  4 +-
 .../KeyboardAvoidingViewExample.js            |  6 +-
 .../NativeAnimationsExample.js                |  4 +-
 .../PointerEvents/PointerEventsExample.js     |  2 +-
 .../js/examples/Pressable/PressableExample.js |  4 +-
 .../rn-tester/js/examples/RTL/RTLExample.js   | 26 +++++--
 .../SafeAreaView/SafeAreaViewExample.js       |  2 +-
 .../examples/ScrollView/ScrollViewExample.js  |  6 +-
 .../SectionList/SectionList-onEndReached.js   |  3 +-
 .../SectionList-onViewableItemsChanged.js     |  7 +-
 .../SectionList/SectionList-scrollable.js     |  9 +--
 .../SectionList/SectionList-withSeparators.js |  4 +-
 .../SwipeableCardExample.js                   |  6 +-
 .../TextInput/TextInputExample.ios.js         | 14 ++--
 .../TextInput/TextInputSharedExamples.js      | 14 ++--
 .../js/examples/Timer/TimerExample.js         |  8 ++-
 .../js/examples/Touchable/TouchableExample.js |  4 +-
 .../TurboModule/SampleTurboModuleExample.js   | 45 +++++++++++-
 74 files changed, 430 insertions(+), 182 deletions(-)

diff --git a/IntegrationTests/AsyncStorageTest.js b/IntegrationTests/AsyncStorageTest.js
index f3aa7ce8052..42bdbd62965 100644
--- a/IntegrationTests/AsyncStorageTest.js
+++ b/IntegrationTests/AsyncStorageTest.js
@@ -33,7 +33,7 @@ const VAL_MERGE_EXPECT = {foo: 1, bar: {hoo: 2, boo: 1}, baz: 2, moo: {a: 3}};
 let done = (result: ?boolean) => {};
 let updateMessage = (message: string) => {};
 
-function runTestCase(description: string, fn) {
+function runTestCase(description: string, fn: () => void) {
   updateMessage(description);
   fn();
 }
@@ -61,7 +61,20 @@ function stringify(
   return JSON.stringify(value);
 }
 
-function expectEqual(lhs, rhs, testname: string) {
+function expectEqual(
+  lhs: ?(any | string | Array<Array<string>>),
+  rhs:
+    | null
+    | string
+    | {
+        bar: {boo: number, hoo: number},
+        baz: number,
+        foo: number,
+        moo: {a: number},
+      }
+    | Array<Array<string>>,
+  testname: string,
+) {
   expectTrue(
     !deepDiffer(lhs, rhs),
     'Error in test ' +
@@ -73,7 +86,10 @@ function expectEqual(lhs, rhs, testname: string) {
   );
 }
 
-function expectAsyncNoError(place, err) {
+function expectAsyncNoError(
+  place: string,
+  err: ?(Error | string | Array<Error>),
+) {
   if (err instanceof Error) {
     err = err.message;
   }
diff --git a/Libraries/Alert/Alert.js b/Libraries/Alert/Alert.js
index d05cf9d6be6..f248e2b9055 100644
--- a/Libraries/Alert/Alert.js
+++ b/Libraries/Alert/Alert.js
@@ -105,7 +105,7 @@ class Alert {
           options && options.onDismiss && options.onDismiss();
         }
       };
-      const onError = errorMessage => console.warn(errorMessage);
+      const onError = (errorMessage: string) => console.warn(errorMessage);
       NativeDialogManagerAndroid.showAlert(config, onError, onAction);
     }
   }
diff --git a/Libraries/Animated/AnimatedEvent.js b/Libraries/Animated/AnimatedEvent.js
index 9aa49926152..af1d660a8de 100644
--- a/Libraries/Animated/AnimatedEvent.js
+++ b/Libraries/Animated/AnimatedEvent.js
@@ -41,7 +41,7 @@ function attachNativeEvent(
   // key path inside the `nativeEvent` object. Ex.: ['contentOffset', 'x'].
   const eventMappings = [];
 
-  const traverse = (value, path) => {
+  const traverse = (value: mixed, path: Array<string>) => {
     if (value instanceof AnimatedValue) {
       value.__makeNative(platformConfig);
 
@@ -94,8 +94,8 @@ function attachNativeEvent(
   };
 }
 
-function validateMapping(argMapping, args) {
-  const validate = (recMapping, recEvt, key) => {
+function validateMapping(argMapping: $ReadOnlyArray<?Mapping>, args: any) {
+  const validate = (recMapping: ?Mapping, recEvt: any, key: string) => {
     if (recMapping instanceof AnimatedValue) {
       invariant(
         typeof recEvt === 'number',
@@ -223,7 +223,10 @@ class AnimatedEvent {
         validatedMapping = true;
       }
 
-      const traverse = (recMapping, recEvt) => {
+      const traverse = (
+        recMapping: ?(Mapping | AnimatedValue),
+        recEvt: any,
+      ) => {
         if (recMapping instanceof AnimatedValue) {
           if (typeof recEvt === 'number') {
             recMapping.setValue(recEvt);
diff --git a/Libraries/Animated/AnimatedImplementation.js b/Libraries/Animated/AnimatedImplementation.js
index 84c47e36a15..32707208a6e 100644
--- a/Libraries/Animated/AnimatedImplementation.js
+++ b/Libraries/Animated/AnimatedImplementation.js
@@ -94,7 +94,7 @@ const _combineCallbacks = function (
   config: $ReadOnly<{...AnimationConfig, ...}>,
 ) {
   if (callback && config.onComplete) {
-    return (...args) => {
+    return (...args: Array<EndResult>) => {
       config.onComplete && config.onComplete(...args);
       callback && callback(...args);
     };
@@ -308,7 +308,7 @@ const sequence = function (
   let current = 0;
   return {
     start: function (callback?: ?EndCallback) {
-      const onComplete = function (result) {
+      const onComplete = function (result: EndResult) {
         if (!result.finished) {
           callback && callback(result);
           return;
@@ -380,7 +380,7 @@ const parallel = function (
       }
 
       animations.forEach((animation, idx) => {
-        const cb = function (endResult) {
+        const cb = function (endResult: EndResult | {finished: boolean}) {
           hasEnded[idx] = true;
           doneCount++;
           if (doneCount === animations.length) {
diff --git a/Libraries/Animated/AnimatedMock.js b/Libraries/Animated/AnimatedMock.js
index af517502197..6efb74fd003 100644
--- a/Libraries/Animated/AnimatedMock.js
+++ b/Libraries/Animated/AnimatedMock.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type {EndResult} from './animations/Animation';
+
 const {AnimatedEvent, attachNativeEvent} = require('./AnimatedEvent');
 const AnimatedImplementation = require('./AnimatedImplementation');
 const AnimatedInterpolation = require('./nodes/AnimatedInterpolation');
@@ -43,7 +45,7 @@ function mockAnimationStart(
     const guardedCallback =
       callback == null
         ? callback
-        : (...args) => {
+        : (...args: Array<EndResult>) => {
             if (inAnimationCallback) {
               console.warn(
                 'Ignoring recursive animation callback when running mock animations',
diff --git a/Libraries/Animated/nodes/AnimatedColor.js b/Libraries/Animated/nodes/AnimatedColor.js
index 8bb31844b22..16a87f52800 100644
--- a/Libraries/Animated/nodes/AnimatedColor.js
+++ b/Libraries/Animated/nodes/AnimatedColor.js
@@ -249,7 +249,7 @@ export default class AnimatedColor extends AnimatedWithChildren {
    */
   addListener(callback: ColorListenerCallback): string {
     const id = String(_uniqueId++);
-    const jointCallback = ({value: number}) => {
+    const jointCallback = ({value: number}: any) => {
       callback(this.__getValue());
     };
     this._listeners[id] = {
diff --git a/Libraries/Animated/nodes/AnimatedValueXY.js b/Libraries/Animated/nodes/AnimatedValueXY.js
index 71d1129c6bc..c54a9d9d6f5 100644
--- a/Libraries/Animated/nodes/AnimatedValueXY.js
+++ b/Libraries/Animated/nodes/AnimatedValueXY.js
@@ -177,7 +177,7 @@ class AnimatedValueXY extends AnimatedWithChildren {
    */
   addListener(callback: ValueXYListenerCallback): string {
     const id = String(_uniqueId++);
-    const jointCallback = ({value: number}) => {
+    const jointCallback = ({value: number}: any) => {
       callback(this.__getValue());
     };
     this._listeners[id] = {
diff --git a/Libraries/BatchedBridge/MessageQueue.js b/Libraries/BatchedBridge/MessageQueue.js
index ed32d725da1..2ae720810ac 100644
--- a/Libraries/BatchedBridge/MessageQueue.js
+++ b/Libraries/BatchedBridge/MessageQueue.js
@@ -252,7 +252,7 @@ class MessageQueue {
       // folly-convertible.  As a special case, if a prop value is a
       // function it is permitted here, and special-cased in the
       // conversion.
-      const isValidArgument = val => {
+      const isValidArgument = (val: mixed) => {
         switch (typeof val) {
           case 'undefined':
           case 'boolean':
@@ -286,7 +286,7 @@ class MessageQueue {
       // Replacement allows normally non-JSON-convertible values to be
       // seen.  There is ambiguity with string values, but in context,
       // it should at least be a strong hint.
-      const replacer = (key, val) => {
+      const replacer = (key: string, val: $FlowFixMe) => {
         const t = typeof val;
         if (t === 'function') {
           return '<<Function ' + val.name + '>>';
diff --git a/Libraries/Components/ScrollView/ScrollView.js b/Libraries/Components/ScrollView/ScrollView.js
index bc7c06aae7b..09ef62817f4 100644
--- a/Libraries/Components/ScrollView/ScrollView.js
+++ b/Libraries/Components/ScrollView/ScrollView.js
@@ -1107,7 +1107,7 @@ class ScrollView extends React.Component<Props, State> {
     }
   };
 
-  _getKeyForIndex(index, childArray) {
+  _getKeyForIndex(index: $FlowFixMe, childArray: $FlowFixMe) {
     const child = childArray[index];
     return child && child.key;
   }
@@ -1140,7 +1140,7 @@ class ScrollView extends React.Component<Props, State> {
     }
   }
 
-  _onStickyHeaderLayout(index, event, key) {
+  _onStickyHeaderLayout(index: $FlowFixMe, event: $FlowFixMe, key: $FlowFixMe) {
     const {stickyHeaderIndices} = this.props;
     if (!stickyHeaderIndices) {
       return;
@@ -1822,7 +1822,7 @@ const styles = StyleSheet.create({
   },
 });
 
-function Wrapper(props, ref) {
+function Wrapper(props, ref: (mixed => mixed) | {current: mixed, ...}) {
   return <ScrollView {...props} scrollViewRef={ref} />;
 }
 Wrapper.displayName = 'ScrollView';
diff --git a/Libraries/Components/Touchable/PooledClass.js b/Libraries/Components/Touchable/PooledClass.js
index 139f1657ea4..7a57583a69c 100644
--- a/Libraries/Components/Touchable/PooledClass.js
+++ b/Libraries/Components/Touchable/PooledClass.js
@@ -18,7 +18,7 @@ import invariant from 'invariant';
  * the Class itself, not an instance. If any others are needed, simply add them
  * here, or in their own files.
  */
-const oneArgumentPooler = function (copyFieldsFrom) {
+const oneArgumentPooler = function (copyFieldsFrom: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
@@ -29,7 +29,7 @@ const oneArgumentPooler = function (copyFieldsFrom) {
   }
 };
 
-const twoArgumentPooler = function (a1, a2) {
+const twoArgumentPooler = function (a1: any, a2: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
@@ -40,7 +40,7 @@ const twoArgumentPooler = function (a1, a2) {
   }
 };
 
-const threeArgumentPooler = function (a1, a2, a3) {
+const threeArgumentPooler = function (a1: any, a2: any, a3: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
@@ -51,7 +51,7 @@ const threeArgumentPooler = function (a1, a2, a3) {
   }
 };
 
-const fourArgumentPooler = function (a1, a2, a3, a4) {
+const fourArgumentPooler = function (a1: any, a2: any, a3: any, a4: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
diff --git a/Libraries/Components/Touchable/Touchable.js b/Libraries/Components/Touchable/Touchable.js
index 47fdfa892d0..b4ec927840f 100644
--- a/Libraries/Components/Touchable/Touchable.js
+++ b/Libraries/Components/Touchable/Touchable.js
@@ -21,7 +21,18 @@ import type {ColorValue} from '../../StyleSheet/StyleSheet';
 import type {EdgeInsetsProp} from '../../StyleSheet/EdgeInsetsPropType';
 import type {PressEvent} from '../../Types/CoreEventTypes';
 
-const extractSingleTouch = nativeEvent => {
+const extractSingleTouch = (nativeEvent: {
+  +changedTouches: $ReadOnlyArray<PressEvent['nativeEvent']>,
+  +force?: number,
+  +identifier: number,
+  +locationX: number,
+  +locationY: number,
+  +pageX: number,
+  +pageY: number,
+  +target: ?number,
+  +timestamp: number,
+  +touches: $ReadOnlyArray<PressEvent['nativeEvent']>,
+}) => {
   const touches = nativeEvent.touches;
   const changedTouches = nativeEvent.changedTouches;
   const hasTouches = touches && touches.length > 0;
diff --git a/Libraries/Components/Touchable/TouchableNativeFeedback.js b/Libraries/Components/Touchable/TouchableNativeFeedback.js
index 910a51c5e30..2064a81c36c 100644
--- a/Libraries/Components/Touchable/TouchableNativeFeedback.js
+++ b/Libraries/Components/Touchable/TouchableNativeFeedback.js
@@ -312,11 +312,11 @@ class TouchableNativeFeedback extends React.Component<Props, State> {
 
 const getBackgroundProp =
   Platform.OS === 'android'
-    ? (background, useForeground) =>
+    ? (background, useForeground: boolean) =>
         useForeground && TouchableNativeFeedback.canUseNativeForeground()
           ? {nativeForegroundAndroid: background}
           : {nativeBackgroundAndroid: background}
-    : (background, useForeground) => null;
+    : (background, useForeground: boolean) => null;
 
 TouchableNativeFeedback.displayName = 'TouchableNativeFeedback';
 
diff --git a/Libraries/Core/Timers/JSTimers.js b/Libraries/Core/Timers/JSTimers.js
index 8682a1dcda5..2ef47d88c0a 100644
--- a/Libraries/Core/Timers/JSTimers.js
+++ b/Libraries/Core/Timers/JSTimers.js
@@ -274,7 +274,7 @@ const JSTimers = {
     const timeout = options && options.timeout;
     const id = _allocateCallback(
       timeout != null
-        ? deadline => {
+        ? (deadline: any) => {
             const timeoutId = requestIdleCallbackTimeouts[id];
             if (timeoutId) {
               JSTimers.clearTimeout(timeoutId);
@@ -364,7 +364,7 @@ const JSTimers = {
         // error one at a time
         for (let ii = 1; ii < errorCount; ii++) {
           JSTimers.setTimeout(
-            (error => {
+            ((error: Error) => {
               throw error;
             }).bind(null, errors[ii]),
             0,
diff --git a/Libraries/Inspector/NetworkOverlay.js b/Libraries/Inspector/NetworkOverlay.js
index a510f357f04..79f2f301a43 100644
--- a/Libraries/Inspector/NetworkOverlay.js
+++ b/Libraries/Inspector/NetworkOverlay.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type {RenderItemProps} from '../Lists/VirtualizedList';
+
 const ScrollView = require('../Components/ScrollView/ScrollView');
 const TouchableHighlight = require('../Components/Touchable/TouchableHighlight');
 const View = require('../Components/View/View');
@@ -326,7 +328,10 @@ class NetworkOverlay extends React.Component<Props, State> {
     WebSocketInterceptor.disableInterception();
   }
 
-  _renderItem = ({item, index}): React.Element<any> => {
+  _renderItem = ({
+    item,
+    index,
+  }: RenderItemProps<NetworkRequestInfo>): React.Element<any> => {
     const tableRowViewStyle = [
       styles.tableRow,
       index % 2 === 1 ? styles.tableRowOdd : styles.tableRowEven,
@@ -358,7 +363,7 @@ class NetworkOverlay extends React.Component<Props, State> {
     );
   };
 
-  _renderItemDetail(id) {
+  _renderItemDetail(id: number) {
     const requestItem = this.state.requests[id];
     const details = Object.keys(requestItem).map(key => {
       if (key === 'id') {
diff --git a/Libraries/Lists/ViewabilityHelper.js b/Libraries/Lists/ViewabilityHelper.js
index 2e000c8f01f..ae91b25ab68 100644
--- a/Libraries/Lists/ViewabilityHelper.js
+++ b/Libraries/Lists/ViewabilityHelper.js
@@ -259,9 +259,13 @@ class ViewabilityHelper {
   }
 
   _onUpdateSync(
-    viewableIndicesToCheck,
-    onViewableItemsChanged,
-    createViewToken,
+    viewableIndicesToCheck: Array<number>,
+    onViewableItemsChanged: ({
+      changed: Array<ViewToken>,
+      viewableItems: Array<ViewToken>,
+      ...
+    }) => void,
+    createViewToken: (index: number, isViewable: boolean) => ViewToken,
   ) {
     // Filter out indices that have gone out of view since this call was scheduled.
     viewableIndicesToCheck = viewableIndicesToCheck.filter(ii =>
diff --git a/Libraries/Lists/VirtualizedList.js b/Libraries/Lists/VirtualizedList.js
index 685a0269e7e..1897a5d3dcb 100644
--- a/Libraries/Lists/VirtualizedList.js
+++ b/Libraries/Lists/VirtualizedList.js
@@ -10,7 +10,7 @@
 
 import type {ScrollResponderType} from '../Components/ScrollView/ScrollView';
 import type {ViewStyleProp} from '../StyleSheet/StyleSheet';
-import type {LayoutEvent} from '../Types/CoreEventTypes';
+import type {LayoutEvent, ScrollEvent} from '../Types/CoreEventTypes';
 import type {
   ViewabilityConfig,
   ViewabilityConfigCallbackPair,
@@ -1713,7 +1713,7 @@ class VirtualizedList extends React.PureComponent<Props, State> {
     }
   }
 
-  _onScrollBeginDrag = (e): void => {
+  _onScrollBeginDrag = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onScrollBeginDrag(e);
     });
@@ -1724,7 +1724,7 @@ class VirtualizedList extends React.PureComponent<Props, State> {
     this.props.onScrollBeginDrag && this.props.onScrollBeginDrag(e);
   };
 
-  _onScrollEndDrag = (e): void => {
+  _onScrollEndDrag = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onScrollEndDrag(e);
     });
@@ -1736,14 +1736,14 @@ class VirtualizedList extends React.PureComponent<Props, State> {
     this.props.onScrollEndDrag && this.props.onScrollEndDrag(e);
   };
 
-  _onMomentumScrollBegin = (e): void => {
+  _onMomentumScrollBegin = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onMomentumScrollBegin(e);
     });
     this.props.onMomentumScrollBegin && this.props.onMomentumScrollBegin(e);
   };
 
-  _onMomentumScrollEnd = (e): void => {
+  _onMomentumScrollEnd = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onMomentumScrollEnd(e);
     });
@@ -2033,7 +2033,12 @@ class CellRenderer extends React.Component<
       );
   };
 
-  _renderElement(renderItem, ListItemComponent, item, index) {
+  _renderElement(
+    renderItem: any,
+    ListItemComponent: any,
+    item: any,
+    index: any,
+  ) {
     if (renderItem && ListItemComponent) {
       console.warn(
         'VirtualizedList: Both ListItemComponent and renderItem props are present. ListItemComponent will take' +
diff --git a/Libraries/Lists/VirtualizedSectionList.js b/Libraries/Lists/VirtualizedSectionList.js
index 396ad7b58ca..f17d6e992a5 100644
--- a/Libraries/Lists/VirtualizedSectionList.js
+++ b/Libraries/Lists/VirtualizedSectionList.js
@@ -392,21 +392,24 @@ class VirtualizedSectionList<
       }
     };
 
-  _updatePropsFor = (cellKey, value) => {
+  _updatePropsFor = (cellKey: string, value: any) => {
     const updateProps = this._updatePropsMap[cellKey];
     if (updateProps != null) {
       updateProps(value);
     }
   };
 
-  _updateHighlightFor = (cellKey, value) => {
+  _updateHighlightFor = (cellKey: string, value: boolean) => {
     const updateHighlight = this._updateHighlightMap[cellKey];
     if (updateHighlight != null) {
       updateHighlight(value);
     }
   };
 
-  _setUpdateHighlightFor = (cellKey, updateHighlightFn) => {
+  _setUpdateHighlightFor = (
+    cellKey: string,
+    updateHighlightFn: ?(boolean) => void,
+  ) => {
     if (updateHighlightFn != null) {
       this._updateHighlightMap[cellKey] = updateHighlightFn;
     } else {
@@ -414,7 +417,7 @@ class VirtualizedSectionList<
     }
   };
 
-  _setUpdatePropsFor = (cellKey, updatePropsFn) => {
+  _setUpdatePropsFor = (cellKey: string, updatePropsFn: ?(boolean) => void) => {
     if (updatePropsFn != null) {
       this._updatePropsMap[cellKey] = updatePropsFn;
     } else {
@@ -449,7 +452,7 @@ class VirtualizedSectionList<
   _updateHighlightMap: {[string]: (boolean) => void} = {};
   _updatePropsMap: {[string]: void | (boolean => void)} = {};
   _listRef: ?React.ElementRef<typeof VirtualizedList>;
-  _captureRef = ref => {
+  _captureRef = (ref: null | React$ElementRef<Class<VirtualizedList>>) => {
     this._listRef = ref;
   };
 }
diff --git a/Libraries/LogBox/Data/LogBoxData.js b/Libraries/LogBox/Data/LogBoxData.js
index 77b13401823..1fb9d59bbec 100644
--- a/Libraries/LogBox/Data/LogBoxData.js
+++ b/Libraries/LogBox/Data/LogBoxData.js
@@ -133,7 +133,7 @@ function handleUpdate(): void {
   }
 }
 
-function appendNewLog(newLog) {
+function appendNewLog(newLog: LogBoxLog) {
   // Don't want store these logs because they trigger a
   // state update when we add them to the store.
   if (isMessageIgnored(newLog.message.content)) {
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js b/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
index e683cea4a3e..bd26449ba0a 100644
--- a/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
+++ b/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
@@ -49,7 +49,7 @@ function getLogBoxSymbolication(): {|
   return (require('../LogBoxSymbolication'): any);
 }
 
-const createStack = methodNames =>
+const createStack = (methodNames: Array<string>) =>
   methodNames.map(methodName => ({
     column: null,
     file: 'file://path/to/file.js',
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js b/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
index 8c16348598c..1d35a1e9867 100644
--- a/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
+++ b/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
@@ -22,7 +22,7 @@ const symbolicateStackTrace: JestMockFn<
   Promise<Array<StackFrame>>,
 > = (require('../../../Core/Devtools/symbolicateStackTrace'): any);
 
-const createStack = methodNames =>
+const createStack = (methodNames: Array<string>) =>
   methodNames.map(methodName => ({
     column: null,
     file: 'file://path/to/file.js',
diff --git a/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js b/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js
index b1227d9a683..08eec15d11f 100644
--- a/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js
+++ b/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js
@@ -8,6 +8,10 @@
  * @format
  */
 
+import type {StackFrame} from '../../Core/NativeExceptionsManager';
+import type {Stack} from '../Data/LogBoxSymbolication';
+import type LogBoxLog from '../Data/LogBoxLog';
+
 import * as React from 'react';
 import StyleSheet from '../../StyleSheet/StyleSheet';
 import Text from '../../Text/Text';
@@ -18,8 +22,6 @@ import LogBoxInspectorStackFrame from './LogBoxInspectorStackFrame';
 import LogBoxInspectorSection from './LogBoxInspectorSection';
 import * as LogBoxStyle from './LogBoxStyle';
 import openFileInEditor from '../../Core/Devtools/openFileInEditor';
-import type {Stack} from '../Data/LogBoxSymbolication';
-import type LogBoxLog from '../Data/LogBoxLog';
 
 type Props = $ReadOnly<{|
   log: LogBoxLog,
@@ -111,7 +113,10 @@ function LogBoxInspectorStackFrames(props: Props): React.Node {
   );
 }
 
-function StackFrameList(props) {
+function StackFrameList(props: {
+  list: Stack | Array<StackFrame>,
+  status: string | 'COMPLETE' | 'FAILED' | 'NONE' | 'PENDING',
+}) {
   return (
     <>
       {props.list.map((frame, index) => {
diff --git a/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js b/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js
index d39afe9f416..28b471938c7 100644
--- a/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js
+++ b/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js
@@ -210,10 +210,10 @@ StaticViewConfigValidator: Invalid static view config for 'RCTView'.
 });
 
 function expectSVCToNotMatchNVC(
-  name,
+  name: string,
   nativeViewConfig,
   staticViewConfig,
-  message,
+  message: string,
 ) {
   const validationResult = StaticViewConfigValidator.validate(
     name,
diff --git a/Libraries/Pressability/Pressability.js b/Libraries/Pressability/Pressability.js
index 4f70f006cf4..54b80e5b0c7 100644
--- a/Libraries/Pressability/Pressability.js
+++ b/Libraries/Pressability/Pressability.js
@@ -255,20 +255,20 @@ const Transitions = Object.freeze({
   },
 });
 
-const isActiveSignal = signal =>
+const isActiveSignal = (signal: TouchState) =>
   signal === 'RESPONDER_ACTIVE_PRESS_IN' ||
   signal === 'RESPONDER_ACTIVE_LONG_PRESS_IN';
 
-const isActivationSignal = signal =>
+const isActivationSignal = (signal: TouchState) =>
   signal === 'RESPONDER_ACTIVE_PRESS_OUT' ||
   signal === 'RESPONDER_ACTIVE_PRESS_IN';
 
-const isPressInSignal = signal =>
+const isPressInSignal = (signal: TouchState) =>
   signal === 'RESPONDER_INACTIVE_PRESS_IN' ||
   signal === 'RESPONDER_ACTIVE_PRESS_IN' ||
   signal === 'RESPONDER_ACTIVE_LONG_PRESS_IN';
 
-const isTerminalSignal = signal =>
+const isTerminalSignal = (signal: TouchSignal) =>
   signal === 'RESPONDER_TERMINATED' || signal === 'RESPONDER_RELEASE';
 
 const DEFAULT_LONG_PRESS_DELAY_MS = 500;
@@ -808,7 +808,14 @@ export default class Pressability {
     }
   }
 
-  _measureCallback = (left, top, width, height, pageX, pageY) => {
+  _measureCallback = (
+    left: number,
+    top: number,
+    width: number,
+    height: number,
+    pageX: number,
+    pageY: number,
+  ) => {
     if (!left && !top && !width && !height && !pageX && !pageY) {
       return;
     }
@@ -918,7 +925,11 @@ export default class Pressability {
   }
 }
 
-function normalizeDelay(delay: ?number, min = 0, fallback = 0): number {
+function normalizeDelay(
+  delay: ?number,
+  min: number = 0,
+  fallback: number = 0,
+): number {
   return Math.max(min, delay ?? fallback);
 }
 
diff --git a/Libraries/Pressability/__tests__/Pressability-test.js b/Libraries/Pressability/__tests__/Pressability-test.js
index cbb48e1acf8..42af85f3dff 100644
--- a/Libraries/Pressability/__tests__/Pressability-test.js
+++ b/Libraries/Pressability/__tests__/Pressability-test.js
@@ -105,7 +105,7 @@ const mockUIManagerMeasure = (options?: {|delay: number|}) => {
   });
 };
 
-const createMockTargetEvent = registrationName => {
+const createMockTargetEvent = (registrationName: string) => {
   const nativeEvent = {
     target: 42,
   };
@@ -132,7 +132,7 @@ const createMockTargetEvent = registrationName => {
   };
 };
 
-const createMockMouseEvent = registrationName => {
+const createMockMouseEvent = (registrationName: string) => {
   const nativeEvent = {
     clientX: 0,
     clientY: 0,
diff --git a/Libraries/ReactNative/PaperUIManager.js b/Libraries/ReactNative/PaperUIManager.js
index ad83e6248af..b331ca2e952 100644
--- a/Libraries/ReactNative/PaperUIManager.js
+++ b/Libraries/ReactNative/PaperUIManager.js
@@ -114,7 +114,7 @@ const UIManagerJS = {
 // $FlowFixMe[prop-missing]
 NativeUIManager.getViewManagerConfig = UIManagerJS.getViewManagerConfig;
 
-function lazifyViewManagerConfig(viewName) {
+function lazifyViewManagerConfig(viewName: string) {
   const viewConfig = getConstants()[viewName];
   viewManagerConfigs[viewName] = viewConfig;
   if (viewConfig.Manager) {
diff --git a/Libraries/Text/Text.js b/Libraries/Text/Text.js
index eafa5e3b277..57b6a2ea82c 100644
--- a/Libraries/Text/Text.js
+++ b/Libraries/Text/Text.js
@@ -8,6 +8,8 @@
  * @format
  */
 
+import type {PressEvent} from '../Types/CoreEventTypes';
+
 import Platform from '../Utilities/Platform';
 import * as PressabilityDebug from '../Pressability/PressabilityDebug';
 import usePressability from '../Pressability/usePressability';
@@ -73,11 +75,11 @@ const Text: React.AbstractComponent<
             pressRectOffset: pressRetentionOffset,
             onLongPress,
             onPress,
-            onPressIn(event) {
+            onPressIn(event: PressEvent) {
               setHighlighted(!suppressHighlighting);
               onPressIn?.(event);
             },
-            onPressOut(event) {
+            onPressOut(event: PressEvent) {
               setHighlighted(false);
               onPressOut?.(event);
             },
@@ -106,25 +108,25 @@ const Text: React.AbstractComponent<
       eventHandlers == null
         ? null
         : {
-            onResponderGrant(event) {
+            onResponderGrant(event: PressEvent) {
               eventHandlers.onResponderGrant(event);
               if (onResponderGrant != null) {
                 onResponderGrant(event);
               }
             },
-            onResponderMove(event) {
+            onResponderMove(event: PressEvent) {
               eventHandlers.onResponderMove(event);
               if (onResponderMove != null) {
                 onResponderMove(event);
               }
             },
-            onResponderRelease(event) {
+            onResponderRelease(event: PressEvent) {
               eventHandlers.onResponderRelease(event);
               if (onResponderRelease != null) {
                 onResponderRelease(event);
               }
             },
-            onResponderTerminate(event) {
+            onResponderTerminate(event: PressEvent) {
               eventHandlers.onResponderTerminate(event);
               if (onResponderTerminate != null) {
                 onResponderTerminate(event);
diff --git a/Libraries/Utilities/HMRClient.js b/Libraries/Utilities/HMRClient.js
index 63da957ef37..16870e57071 100644
--- a/Libraries/Utilities/HMRClient.js
+++ b/Libraries/Utilities/HMRClient.js
@@ -256,7 +256,7 @@ Error: ${e.message}`;
   },
 };
 
-function setHMRUnavailableReason(reason) {
+function setHMRUnavailableReason(reason: string) {
   invariant(hmrClient, 'Expected HMRClient.setup() call at startup.');
   if (hmrUnavailableReason !== null) {
     // Don't show more than one warning.
@@ -273,7 +273,7 @@ function setHMRUnavailableReason(reason) {
   }
 }
 
-function registerBundleEntryPoints(client) {
+function registerBundleEntryPoints(client: MetroHMRClient) {
   if (hmrUnavailableReason != null) {
     DevSettings.reload('Bundle Splitting – Metro disconnected');
     return;
@@ -290,7 +290,7 @@ function registerBundleEntryPoints(client) {
   }
 }
 
-function flushEarlyLogs(client) {
+function flushEarlyLogs(client: MetroHMRClient) {
   try {
     pendingLogs.forEach(([level, data]) => {
       HMRClient.log(level, data);
diff --git a/Libraries/Utilities/ReactNativeTestTools.js b/Libraries/Utilities/ReactNativeTestTools.js
index 4c7bc91b419..dfbb46780bc 100644
--- a/Libraries/Utilities/ReactNativeTestTools.js
+++ b/Libraries/Utilities/ReactNativeTestTools.js
@@ -180,7 +180,9 @@ function renderAndEnforceStrictMode(element: React.Node): any {
 }
 
 function renderWithStrictMode(element: React.Node): ReactTestRendererType {
-  const WorkAroundBugWithStrictModeInTestRenderer = prps => prps.children;
+  const WorkAroundBugWithStrictModeInTestRenderer = (prps: {
+    children: React.Node,
+  }) => prps.children;
   const StrictMode = (React: $FlowFixMe).StrictMode;
   return ReactTestRenderer.create(
     <WorkAroundBugWithStrictModeInTestRenderer>
diff --git a/Libraries/Vibration/Vibration.js b/Libraries/Vibration/Vibration.js
index 840527de0de..f862235d79e 100644
--- a/Libraries/Vibration/Vibration.js
+++ b/Libraries/Vibration/Vibration.js
@@ -40,7 +40,7 @@ function vibrateByPattern(pattern: Array<number>, repeat: boolean = false) {
 }
 
 function vibrateScheduler(
-  id,
+  id: number,
   pattern: Array<number>,
   repeat: boolean,
   nextIndex: number,
diff --git a/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js b/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js
index c0c1969a737..50a8b3c8bfa 100644
--- a/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js
+++ b/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js
@@ -10,6 +10,11 @@
 
 'use strict';
 
+import type {
+  PressEvent,
+  ScrollEvent,
+} from 'react-native/Libraries/Types/CoreEventTypes';
+
 const BatchedBridge = require('react-native/Libraries/BatchedBridge/BatchedBridge');
 const React = require('react');
 
@@ -26,8 +31,6 @@ const {ScrollListener} = NativeModules;
 
 const NUM_ITEMS = 100;
 
-import type {PressEvent} from 'react-native/Libraries/Types/CoreEventTypes';
-
 // Shared by integration tests for ScrollView and HorizontalScrollView
 
 let scrollViewApp: ScrollViewTestApp | HorizontalScrollViewTestApp;
@@ -61,28 +64,28 @@ const getInitialState = function () {
   };
 };
 
-const onScroll = function (e) {
+const onScroll = function (e: ScrollEvent) {
   ScrollListener.onScroll(
     e.nativeEvent.contentOffset.x,
     e.nativeEvent.contentOffset.y,
   );
 };
 
-const onScrollBeginDrag = function (e) {
+const onScrollBeginDrag = function (e: ScrollEvent) {
   ScrollListener.onScrollBeginDrag(
     e.nativeEvent.contentOffset.x,
     e.nativeEvent.contentOffset.y,
   );
 };
 
-const onScrollEndDrag = function (e) {
+const onScrollEndDrag = function (e: ScrollEvent) {
   ScrollListener.onScrollEndDrag(
     e.nativeEvent.contentOffset.x,
     e.nativeEvent.contentOffset.y,
   );
 };
 
-const onItemPress = function (itemNumber) {
+const onItemPress = function (itemNumber: number) {
   ScrollListener.onItemPress(itemNumber);
 };
 
diff --git a/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js b/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js
index b8f5cdb32e8..5784f9f2f26 100644
--- a/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js
+++ b/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js
@@ -70,7 +70,7 @@ export class HeaderWriter {
     this.stream.write('struct UnknownRequest;\n\n');
 
     const namespaceMap: Map<string, Array<Type | Command | Event>> = new Map();
-    const addToMap = function (type) {
+    const addToMap = function (type: Type | Command | Event) {
       const domain = type.domain;
       let types = namespaceMap.get(domain);
       if (!types) {
diff --git a/ReactCommon/hermes/inspector/tools/msggen/src/index.js b/ReactCommon/hermes/inspector/tools/msggen/src/index.js
index eb9a4f3ba96..1a137ac7170 100644
--- a/ReactCommon/hermes/inspector/tools/msggen/src/index.js
+++ b/ReactCommon/hermes/inspector/tools/msggen/src/index.js
@@ -32,7 +32,7 @@ type Descriptor = {|
   events: Array<Event>,
 |};
 
-function mergeDomains(original, extra) {
+function mergeDomains(original: any, extra: any) {
   return {...original, domains: original.domains.concat(extra.domains)};
 }
 
@@ -186,7 +186,7 @@ function filterReachableFromRoots(
 
   // Sort commands and events so the code is easier to read. Types have to be
   // topologically sorted as explained above.
-  const comparator = (a, b) => {
+  const comparator = (a: Command | Event, b: Command | Event) => {
     const id1 = a.getDebuggerName();
     const id2 = b.getDebuggerName();
     return id1 < id2 ? -1 : id1 > id2 ? 1 : 0;
diff --git a/packages/react-native-codegen/src/generators/RNCodegen.js b/packages/react-native-codegen/src/generators/RNCodegen.js
index dd9cd128395..78004999db3 100644
--- a/packages/react-native-codegen/src/generators/RNCodegen.js
+++ b/packages/react-native-codegen/src/generators/RNCodegen.js
@@ -198,7 +198,7 @@ module.exports = {
   ): boolean {
     schemaValidator.validate(schema);
 
-    function composePath(intermediate) {
+    function composePath(intermediate: string) {
       return path.join(outputDirectory, intermediate, libraryName);
     }
 
diff --git a/packages/react-native-codegen/src/generators/components/CppHelpers.js b/packages/react-native-codegen/src/generators/components/CppHelpers.js
index 92ee6c2529b..608fd6d9812 100644
--- a/packages/react-native-codegen/src/generators/components/CppHelpers.js
+++ b/packages/react-native-codegen/src/generators/components/CppHelpers.js
@@ -57,7 +57,13 @@ function getImports(
 ): Set<string> {
   const imports: Set<string> = new Set();
 
-  function addImportsForNativeName(name) {
+  function addImportsForNativeName(
+    name:
+      | 'ColorPrimitive'
+      | 'EdgeInsetsPrimitive'
+      | 'ImageSourcePrimitive'
+      | 'PointPrimitive',
+  ) {
     switch (name) {
       case 'ColorPrimitive':
         return;
diff --git a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js
index 59690c61e6e..cb82e3903b0 100644
--- a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js
+++ b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {EventTypeShape} from '../../CodegenSchema';
 
 const {generateEventStructName} = require('./CppHelpers.js');
 
@@ -90,7 +91,11 @@ void ${className}EventEmitter::${eventName}() const {
 }
 `.trim();
 
-function generateSetter(variableName, propertyName, propertyParts) {
+function generateSetter(
+  variableName: string,
+  propertyName: string,
+  propertyParts: $ReadOnlyArray<string>,
+) {
   const trailingPeriod = propertyParts.length === 0 ? '' : '.';
   const eventChain = `event.${propertyParts.join(
     '.',
@@ -99,7 +104,11 @@ function generateSetter(variableName, propertyName, propertyParts) {
   return `${variableName}.setProperty(runtime, "${propertyName}", ${eventChain}`;
 }
 
-function generateEnumSetter(variableName, propertyName, propertyParts) {
+function generateEnumSetter(
+  variableName: string,
+  propertyName: string,
+  propertyParts: $ReadOnlyArray<string>,
+) {
   const trailingPeriod = propertyParts.length === 0 ? '' : '.';
   const eventChain = `event.${propertyParts.join(
     '.',
@@ -177,7 +186,7 @@ function generateSetters(
   return propSetters;
 }
 
-function generateEvent(componentName: string, event): string {
+function generateEvent(componentName: string, event: EventTypeShape): string {
   // This is a gross hack necessary because native code is sending
   // events named things like topChange to JS which is then converted back to
   // call the onChange prop. We should be consistent throughout the system.
diff --git a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js
index 8eba4d79f6a..269567575c0 100644
--- a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js
+++ b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js
@@ -135,7 +135,11 @@ function getNativeTypeFromAnnotation(
       throw new Error(`Received invalid event property type ${type}`);
   }
 }
-function generateEnum(structs, options, nameParts) {
+function generateEnum(
+  structs: StructsMap,
+  options: $ReadOnlyArray<string>,
+  nameParts: Array<string>,
+) {
   const structName = generateEventStructName(nameParts);
   const fields = options
     .map((option, index) => `${toSafeCppString(option)}`)
@@ -218,7 +222,10 @@ function generateStruct(
   );
 }
 
-function generateStructs(componentName: string, component): string {
+function generateStructs(
+  componentName: string,
+  component: ComponentShape,
+): string {
   const structs: StructsMap = new Map();
 
   component.events.forEach(event => {
@@ -244,7 +251,10 @@ function generateEvent(componentName: string, event: EventTypeShape): string {
 
   return `void ${event.name}() const;`;
 }
-function generateEvents(componentName: string, component): string {
+function generateEvents(
+  componentName: string,
+  component: ComponentShape,
+): string {
   return component.events
     .map(event => generateEvent(componentName, event))
     .join('\n\n' + '  ');
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js b/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js
index 145b8467757..ad9d6aac61f 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js
@@ -74,7 +74,7 @@ function generatePropsString(componentName: string, component: ComponentShape) {
     .join(',\n' + '    ');
 }
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   const extendString =
     ' ' +
     component.extendsProps
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsH.js b/packages/react-native-codegen/src/generators/components/GeneratePropsH.js
index fc8202a1c09..26521b0cbb1 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsH.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsH.js
@@ -9,6 +9,16 @@
  */
 
 'use strict';
+import type {
+  StringTypeAnnotation,
+  ReservedPropTypeAnnotation,
+  ObjectTypeAnnotation,
+  Int32TypeAnnotation,
+  FloatTypeAnnotation,
+  DoubleTypeAnnotation,
+  ComponentShape,
+  BooleanTypeAnnotation,
+} from '../../CodegenSchema';
 
 const {
   convertDefaultTypeToString,
@@ -257,7 +267,7 @@ static inline std::string toString(const ${enumMask} &value) {
 }
 `.trim();
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   if (component.extendsProps.length === 0) {
     throw new Error('Invalid: component.extendsProps is empty');
   }
@@ -286,7 +296,29 @@ function getClassExtendString(component): string {
 
 function getNativeTypeFromAnnotation(
   componentName: string,
-  prop,
+  prop:
+    | NamedShape<PropTypeAnnotation>
+    | {
+        name: string,
+        typeAnnotation:
+          | $FlowFixMe
+          | DoubleTypeAnnotation
+          | FloatTypeAnnotation
+          | BooleanTypeAnnotation
+          | Int32TypeAnnotation
+          | StringTypeAnnotation
+          | ObjectTypeAnnotation<PropTypeAnnotation>
+          | ReservedPropTypeAnnotation
+          | {
+              +default: string,
+              +options: $ReadOnlyArray<string>,
+              +type: 'StringEnumTypeAnnotation',
+            }
+          | {
+              +elementType: ObjectTypeAnnotation<PropTypeAnnotation>,
+              +type: 'ArrayTypeAnnotation',
+            },
+      },
   nameParts: $ReadOnlyArray<string>,
 ): string {
   const typeAnnotation = prop.typeAnnotation;
@@ -400,7 +432,10 @@ function generateArrayEnumString(
   });
 }
 
-function generateStringEnum(componentName, prop) {
+function generateStringEnum(
+  componentName: string,
+  prop: NamedShape<PropTypeAnnotation>,
+) {
   const typeAnnotation = prop.typeAnnotation;
   if (typeAnnotation.type === 'StringEnumTypeAnnotation') {
     const values: $ReadOnlyArray<string> = typeAnnotation.options;
@@ -435,7 +470,10 @@ function generateStringEnum(componentName, prop) {
   return '';
 }
 
-function generateIntEnum(componentName, prop) {
+function generateIntEnum(
+  componentName: string,
+  prop: NamedShape<PropTypeAnnotation>,
+) {
   const typeAnnotation = prop.typeAnnotation;
   if (typeAnnotation.type === 'Int32EnumTypeAnnotation') {
     const values: $ReadOnlyArray<number> = typeAnnotation.options;
@@ -476,7 +514,10 @@ function generateIntEnum(componentName, prop) {
   return '';
 }
 
-function generateEnumString(componentName: string, component): string {
+function generateEnumString(
+  componentName: string,
+  component: ComponentShape,
+): string {
   return component.props
     .map(prop => {
       if (
@@ -567,7 +608,13 @@ function getLocalImports(
 ): Set<string> {
   const imports: Set<string> = new Set();
 
-  function addImportsForNativeName(name) {
+  function addImportsForNativeName(
+    name:
+      | 'ColorPrimitive'
+      | 'EdgeInsetsPrimitive'
+      | 'ImageSourcePrimitive'
+      | 'PointPrimitive',
+  ) {
     switch (name) {
       case 'ColorPrimitive':
         imports.add('#include <react/renderer/graphics/Color.h>');
@@ -635,7 +682,10 @@ function getLocalImports(
   return imports;
 }
 
-function generateStructsForComponent(componentName: string, component): string {
+function generateStructsForComponent(
+  componentName: string,
+  component: ComponentShape,
+): string {
   const structs = generateStructs(componentName, component.props, []);
   const structArray = Array.from(structs.values());
   if (structArray.length < 1) {
@@ -646,8 +696,8 @@ function generateStructsForComponent(componentName: string, component): string {
 
 function generateStructs(
   componentName: string,
-  properties,
-  nameParts,
+  properties: $ReadOnlyArray<NamedShape<PropTypeAnnotation>>,
+  nameParts: Array<string>,
 ): StructsMap {
   const structs: StructsMap = new Map();
   properties.forEach(prop => {
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js
index 17bdbda66ad..f39fe2a51d9 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {CommandParamTypeAnnotation} from '../../CodegenSchema';
 
 import type {
   NamedShape,
@@ -170,7 +171,10 @@ function generatePropCasesString(
     }`;
 }
 
-function getCommandArgJavaType(param, index) {
+function getCommandArgJavaType(
+  param: NamedShape<CommandParamTypeAnnotation>,
+  index: number,
+) {
   const {typeAnnotation} = param;
 
   switch (typeAnnotation.type) {
@@ -229,7 +233,7 @@ function generateCommandCasesString(
   return commandMethods;
 }
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   const extendString = component.extendsProps
     .map(extendProps => {
       switch (extendProps.type) {
@@ -251,7 +255,7 @@ function getClassExtendString(component): string {
   return extendString;
 }
 
-function getDelegateImports(component) {
+function getDelegateImports(component: ComponentShape) {
   const imports = getImports(component, 'delegate');
   // The delegate needs ReadableArray for commands always.
   // The interface doesn't always need it
@@ -265,7 +269,10 @@ function getDelegateImports(component) {
   return imports;
 }
 
-function generateMethods(propsString, commandsString): string {
+function generateMethods(
+  propsString: string,
+  commandsString: null | string,
+): string {
   return [
     PropSetterTemplate({propCases: propsString}),
     commandsString != null
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js
index 581564d10fc..5afeeb6e51d 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {CommandParamTypeAnnotation} from '../../CodegenSchema';
 
 import type {
   NamedShape,
@@ -56,13 +57,13 @@ public interface ${className}<T extends ${extendClasses}> {
 }
 `;
 
-function addNullable(imports) {
+function addNullable(imports: Set<string>) {
   imports.add('import androidx.annotation.Nullable;');
 }
 
 function getJavaValueForProp(
   prop: NamedShape<PropTypeAnnotation>,
-  imports,
+  imports: Set<string>,
 ): string {
   const typeAnnotation = prop.typeAnnotation;
 
@@ -126,7 +127,7 @@ function getJavaValueForProp(
   }
 }
 
-function generatePropsString(component: ComponentShape, imports) {
+function generatePropsString(component: ComponentShape, imports: Set<string>) {
   if (component.props.length === 0) {
     return '// No props';
   }
@@ -140,7 +141,7 @@ function generatePropsString(component: ComponentShape, imports) {
     .join('\n' + '  ');
 }
 
-function getCommandArgJavaType(param) {
+function getCommandArgJavaType(param: NamedShape<CommandParamTypeAnnotation>) {
   const {typeAnnotation} = param;
 
   switch (typeAnnotation.type) {
@@ -198,7 +199,7 @@ function generateCommandsString(
     .join('\n' + '  ');
 }
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   const extendString = component.extendsProps
     .map(extendProps => {
       switch (extendProps.type) {
diff --git a/packages/react-native-codegen/src/generators/components/GenerateTests.js b/packages/react-native-codegen/src/generators/components/GenerateTests.js
index dbaffefdd72..cfefaa318bd 100644
--- a/packages/react-native-codegen/src/generators/components/GenerateTests.js
+++ b/packages/react-native-codegen/src/generators/components/GenerateTests.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {PropTypeAnnotation, ComponentShape} from '../../CodegenSchema';
 
 import type {SchemaType} from '../../CodegenSchema';
 const {getImports, toSafeCppString} = require('./CppHelpers');
@@ -76,7 +77,10 @@ TEST(${componentName}_${testName}, etc) {
 }
 `;
 
-function getTestCasesForProp(propName, typeAnnotation) {
+function getTestCasesForProp(
+  propName: string,
+  typeAnnotation: PropTypeAnnotation,
+) {
   const cases = [];
   if (typeAnnotation.type === 'StringEnumTypeAnnotation') {
     typeAnnotation.options.forEach(option =>
@@ -134,7 +138,7 @@ function getTestCasesForProp(propName, typeAnnotation) {
   return cases;
 }
 
-function generateTestsString(name, component) {
+function generateTestsString(name: string, component: ComponentShape) {
   function createTest({testName, propName, propValue, raw = false}: TestCase) {
     const value =
       !raw && typeof propValue === 'string' ? `"${propValue}"` : propValue;
diff --git a/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js b/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js
index 5d7d481383b..046e86b1c65 100644
--- a/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js
+++ b/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js
@@ -127,7 +127,7 @@ function serializeArg(
     realTypeAnnotation = resolveAlias(realTypeAnnotation.name);
   }
 
-  function wrap(callback) {
+  function wrap(callback: (val: string) => string) {
     const val = `args[${index}]`;
     const expression = callback(val);
 
diff --git a/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js b/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js
index d21f33c9283..1f518d3f47e 100644
--- a/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js
+++ b/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js
@@ -119,7 +119,7 @@ function translatePrimitiveJSTypeToCpp(
     realTypeAnnotation = resolveAlias(realTypeAnnotation.name);
   }
 
-  function wrap(type) {
+  function wrap(type: string) {
     return nullable ? `std::optional<${type}>` : type;
   }
 
diff --git a/packages/react-native-codegen/src/parsers/flow/components/props.js b/packages/react-native-codegen/src/parsers/flow/components/props.js
index 1c7982da781..003f47bed2e 100644
--- a/packages/react-native-codegen/src/parsers/flow/components/props.js
+++ b/packages/react-native-codegen/src/parsers/flow/components/props.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {ASTNode} from '../utils';
 
 const {getValueFromTypes} = require('../utils.js');
 
@@ -177,7 +178,7 @@ function getTypeAnnotationForArray(
 
 function getTypeAnnotation(
   name: string,
-  annotation,
+  annotation: $FlowFixMe | ASTNode,
   defaultValue: $FlowFixMe | null,
   withNullDefault: boolean,
   types: TypeDeclarationMap,
diff --git a/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js b/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js
index 2601d945f74..25c9d178d7d 100644
--- a/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js
+++ b/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js
@@ -712,7 +712,7 @@ describe('Flow Module Parser', () => {
       const RETURN_TYPE_DESCRIPTION = IS_RETURN_TYPE_NULLABLE
         ? 'a nullable'
         : 'a non-nullable';
-      const annotateRet = retType =>
+      const annotateRet = (retType: string) =>
         IS_RETURN_TYPE_NULLABLE ? `?${retType}` : retType;
 
       function parseReturnType(
@@ -927,7 +927,7 @@ describe('Flow Module Parser', () => {
                   ? 'an optional'
                   : 'a required';
 
-              function annotateProp(propName, propType) {
+              function annotateProp(propName: string, propType: string) {
                 if (nullable && optional) {
                   return `${propName}?: ?${propType}`;
                 }
@@ -1229,7 +1229,7 @@ describe('Flow Module Parser', () => {
   });
 });
 
-function parseModule(source) {
+function parseModule(source: string) {
   const schema = parseString(source, `${MODULE_NAME}.js`);
   const module = schema.modules.NativeFoo;
   invariant(
diff --git a/packages/react-native-codegen/src/parsers/flow/modules/index.js b/packages/react-native-codegen/src/parsers/flow/modules/index.js
index 10153679a65..38ce80db4e7 100644
--- a/packages/react-native-codegen/src/parsers/flow/modules/index.js
+++ b/packages/react-native-codegen/src/parsers/flow/modules/index.js
@@ -549,7 +549,7 @@ function buildPropertySchema(
   };
 }
 
-function isModuleInterface(node) {
+function isModuleInterface(node: $FlowFixMe) {
   return (
     node.type === 'InterfaceDeclaration' &&
     node.extends.length === 1 &&
diff --git a/packages/react-native-codegen/src/parsers/typescript/components/props.js b/packages/react-native-codegen/src/parsers/typescript/components/props.js
index 68d1d85e0b3..1d58f0d2445 100644
--- a/packages/react-native-codegen/src/parsers/typescript/components/props.js
+++ b/packages/react-native-codegen/src/parsers/typescript/components/props.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {ASTNode} from '../utils';
 
 const {getValueFromTypes} = require('../utils.js');
 
@@ -221,7 +222,7 @@ function getTypeAnnotationForArray(
 
 function getTypeAnnotation(
   name: string,
-  annotation,
+  annotation: $FlowFixMe | ASTNode,
   defaultValue: $FlowFixMe | null,
   withNullDefault: boolean,
   types: TypeDeclarationMap,
diff --git a/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js b/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js
index caa2043ca55..99b7702f5fd 100644
--- a/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js
+++ b/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js
@@ -714,7 +714,7 @@ describe('TypeScript Module Parser', () => {
       const RETURN_TYPE_DESCRIPTION = IS_RETURN_TYPE_NULLABLE
         ? 'a nullable'
         : 'a non-nullable';
-      const annotateRet = retType =>
+      const annotateRet = (retType: string) =>
         IS_RETURN_TYPE_NULLABLE ? `${retType} | null | void` : retType;
 
       function parseReturnType(
@@ -927,7 +927,7 @@ describe('TypeScript Module Parser', () => {
                   ? 'an optional'
                   : 'a required';
 
-              function annotateProp(propName, propType) {
+              function annotateProp(propName: string, propType: string) {
                 if (nullable && optional) {
                   return `${propName}?: ${propType} | null | void`;
                 }
@@ -1231,7 +1231,7 @@ describe('TypeScript Module Parser', () => {
   });
 });
 
-function parseModule(source) {
+function parseModule(source: string) {
   const schema = parseString(source, `${MODULE_NAME}.ts`);
   const module = schema.modules.NativeFoo;
   invariant(
diff --git a/packages/react-native-codegen/src/parsers/typescript/modules/index.js b/packages/react-native-codegen/src/parsers/typescript/modules/index.js
index 66041f980df..a2048bbdc82 100644
--- a/packages/react-native-codegen/src/parsers/typescript/modules/index.js
+++ b/packages/react-native-codegen/src/parsers/typescript/modules/index.js
@@ -551,7 +551,7 @@ function buildPropertySchema(
   };
 }
 
-function isModuleInterface(node) {
+function isModuleInterface(node: $FlowFixMe) {
   return (
     node.type === 'TSInterfaceDeclaration' &&
     node.extends.length === 1 &&
diff --git a/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js b/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js
index 171c61b2b0c..3788016c810 100644
--- a/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js
+++ b/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js
@@ -189,7 +189,7 @@ class Circle extends React.Component<any, any> {
       </Animated.View>
     );
   }
-  _toggleIsActive = velocity => {
+  _toggleIsActive = (velocity: void) => {
     const config = {tension: 30, friction: 7};
     if (this.state.isActive) {
       Animated.spring(this.props.openVal, {
@@ -311,7 +311,7 @@ function distance(p1: Point, p2: Point): number {
   return dx * dx + dy * dy;
 }
 
-function moveToClosest({activeKey, keys, restLayouts}, position) {
+function moveToClosest({activeKey, keys, restLayouts}: any, position: Point) {
   const activeIdx = -1;
   let closestIdx = activeIdx;
   let minDist = Infinity;
diff --git a/packages/rn-tester/js/examples/Button/ButtonExample.js b/packages/rn-tester/js/examples/Button/ButtonExample.js
index dd97ad5a78f..cc04f1e0bea 100644
--- a/packages/rn-tester/js/examples/Button/ButtonExample.js
+++ b/packages/rn-tester/js/examples/Button/ButtonExample.js
@@ -15,7 +15,7 @@ const React = require('react');
 const {Alert, Button, View, StyleSheet} = require('react-native');
 const {RNTesterThemeContext} = require('../../components/RNTesterTheme');
 
-function onButtonPress(buttonName) {
+function onButtonPress(buttonName: string) {
   Alert.alert(`Your application has been ${buttonName}!`);
 }
 
diff --git a/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js b/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
index 4faee1f310a..6e8eb5f8851 100644
--- a/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
+++ b/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
@@ -8,6 +8,7 @@
  * @flow
  */
 
+import type {RenderItemProps} from 'react-native/Libraries/Lists/VirtualizedList';
 import type {
   ViewStyleProp,
   TextStyle,
@@ -73,7 +74,7 @@ const TableRow = React.memo(
   },
 );
 
-function renderTableRow({item}) {
+function renderTableRow({item}: RenderItemProps<PlatformTestResult>) {
   return <TableRow testResult={item} />;
 }
 
diff --git a/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js b/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js
index 99208285875..0fa7ceb46b5 100644
--- a/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js
+++ b/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js
@@ -60,19 +60,19 @@ export function check_PointerEvent(
   // * if the attribute is "readonly", it cannot be changed
   // TA: 1.1, 1.2
   const idl_type_check = {
-    long: function (v) {
+    long: function (v: any) {
       return typeof v === 'number' && Math.round(v) === v;
     },
-    float: function (v) {
+    float: function (v: any) {
       return typeof v === 'number';
     },
-    string: function (v) {
+    string: function (v: any) {
       return typeof v === 'string';
     },
-    boolean: function (v) {
+    boolean: function (v: any) {
       return typeof v === 'boolean';
     },
-    object: function (v) {
+    object: function (v: any) {
       return typeof v === 'object';
     },
   };
@@ -189,7 +189,8 @@ export function useTestEventHandler(
   handler: (event: any, eventName: string) => void,
 ): ViewProps {
   const eventProps: any = useMemo(() => {
-    const handlerFactory = eventName => event => handler(event, eventName);
+    const handlerFactory = (eventName: string) => (event: any) =>
+      handler(event, eventName);
     const props = {};
     for (const eventName of eventNames) {
       const eventPropName =
diff --git a/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js b/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js
index 5cf7c0e8650..d105decc169 100644
--- a/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js
+++ b/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js
@@ -8,6 +8,7 @@
  * @flow
  */
 
+import type {PointerEvent} from 'react-native/Libraries/Types/CoreEventTypes';
 import {Button, StyleSheet, ScrollView, View, Text} from 'react-native';
 import * as React from 'react';
 import type {ViewProps} from 'react-native/Libraries/Components/View/ViewPropTypes';
@@ -55,7 +56,7 @@ function EventfulView(props: {|
   } = props;
   const [tag, setTag] = React.useState('');
 
-  const eventLog = eventName => event => {
+  const eventLog = (eventName: string) => (event: PointerEvent) => {
     // $FlowFixMe Using private property
     log(`${name} - ${eventName} - target: ${event.target._nativeTag}`);
   };
@@ -159,7 +160,7 @@ function PointerEventScaffolding({
 }) {
   const [eventsLog, setEventsLog] = React.useState('');
   const clear = () => setEventsLog('');
-  const log = eventStr => {
+  const log = (eventStr: string) => {
     setEventsLog(currentEventsLog => `${eventStr}\n${currentEventsLog}`);
   };
   return (
diff --git a/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js b/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js
index c2b206020a7..7d5c0437d3e 100644
--- a/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js
+++ b/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js
@@ -16,7 +16,8 @@ import * as React from 'react';
 export function FlatList_onEndReached(): React.Node {
   const [output, setOutput] = React.useState('');
   const exampleProps = {
-    onEndReached: info => setOutput('onEndReached'),
+    onEndReached: (info: {distanceFromEnd: number, ...}) =>
+      setOutput('onEndReached'),
     onEndReachedThreshold: 0,
   };
   const ref = React.useRef(null);
diff --git a/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js b/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js
index b7328846298..9a0f0294891 100644
--- a/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js
+++ b/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js
@@ -15,8 +15,13 @@ import {StyleSheet, View, Text} from 'react-native';
 import * as React from 'react';
 
 const Separator =
-  (defaultColor, highlightColor) =>
-  ({leadingItem, trailingItem, highlighted, hasBeenHighlighted}) => {
+  (defaultColor: string, highlightColor: string) =>
+  ({
+    leadingItem,
+    trailingItem,
+    highlighted,
+    hasBeenHighlighted,
+  }: $FlowFixMe) => {
     const text = `Separator for leading ${leadingItem} and trailing ${trailingItem} has ${
       !hasBeenHighlighted ? 'not ' : ''
     }been pressed`;
diff --git a/packages/rn-tester/js/examples/Image/ImageExample.js b/packages/rn-tester/js/examples/Image/ImageExample.js
index c1c4ef96bff..eacc26ec275 100644
--- a/packages/rn-tester/js/examples/Image/ImageExample.js
+++ b/packages/rn-tester/js/examples/Image/ImageExample.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type {LayoutEvent} from 'react-native/Libraries/Types/CoreEventTypes';
+
 const React = require('react');
 
 const {
@@ -451,7 +453,7 @@ class OnLayoutExample extends React.Component<
     layoutHandlerMessage: 'No Message',
   };
 
-  onLayoutHandler = event => {
+  onLayoutHandler = (event: LayoutEvent) => {
     this.setState({
       width: this.state.width,
       height: this.state.height,
diff --git a/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js b/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js
index 627b5751f75..7a86ed1d872 100644
--- a/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js
+++ b/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js
@@ -42,7 +42,11 @@ const TextInputForm = () => {
   );
 };
 
-const CloseButton = props => {
+const CloseButton = (
+  props:
+    | {behavior: any, setModalOpen: any}
+    | {behavior: string, setModalOpen: any},
+) => {
   return (
     <View
       style={[
diff --git a/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js b/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js
index 13143091087..c5dabd8589c 100644
--- a/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js
+++ b/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type AnimatedValue from 'react-native/Libraries/Animated/nodes/AnimatedValue';
+
 const React = require('react');
 
 const {
@@ -313,7 +315,7 @@ class TrackingExample extends React.Component<
     this.state.toJS.setValue(nextValue);
   };
 
-  renderBlock = (anim, dest) => [
+  renderBlock = (anim: any | AnimatedValue, dest: any | AnimatedValue) => [
     <Animated.View
       key="line"
       style={[styles.line, {transform: [{translateX: dest}]}]}
diff --git a/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js b/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js
index 22e4f047779..57654c0687b 100644
--- a/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js
+++ b/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js
@@ -268,7 +268,7 @@ const exampleClasses: Array<ExampleClass> = [
   },
 ];
 
-const infoToExample = info => {
+const infoToExample = (info: ExampleClass) => {
   return {
     title: info.title,
     description: info.description,
diff --git a/packages/rn-tester/js/examples/Pressable/PressableExample.js b/packages/rn-tester/js/examples/Pressable/PressableExample.js
index f4629a8bb29..b13987f1246 100644
--- a/packages/rn-tester/js/examples/Pressable/PressableExample.js
+++ b/packages/rn-tester/js/examples/Pressable/PressableExample.js
@@ -84,7 +84,7 @@ function TextOnPressBox() {
 function PressableFeedbackEvents() {
   const [eventLog, setEventLog] = useState([]);
 
-  function appendEvent(eventName) {
+  function appendEvent(eventName: string) {
     const limit = 6;
     setEventLog(current => {
       return [eventName].concat(current.slice(0, limit - 1));
@@ -120,7 +120,7 @@ function PressableFeedbackEvents() {
 function PressableDelayEvents() {
   const [eventLog, setEventLog] = useState([]);
 
-  function appendEvent(eventName) {
+  function appendEvent(eventName: string) {
     const limit = 6;
     const newEventLog = eventLog.slice(0, limit - 1);
     newEventLog.unshift(eventName);
diff --git a/packages/rn-tester/js/examples/RTL/RTLExample.js b/packages/rn-tester/js/examples/RTL/RTLExample.js
index 25415fe0c30..f9bb40b4b3a 100644
--- a/packages/rn-tester/js/examples/RTL/RTLExample.js
+++ b/packages/rn-tester/js/examples/RTL/RTLExample.js
@@ -43,7 +43,7 @@ const IMAGE_SIZE = [IMAGE_DIMENSION, IMAGE_DIMENSION];
 
 const IS_RTL = I18nManager.isRTL;
 
-function ListItem(props) {
+function ListItem(props: {imageSource: number}) {
   return (
     <View style={styles.row}>
       <View style={styles.column1}>
@@ -127,7 +127,10 @@ const IconsExample = withRTLState(({isRTL, setRTL}) => {
   );
 });
 
-function AnimationBlock(props) {
+function AnimationBlock(props: {
+  imgStyle: {transform: Array<{scaleX: number} | {translateX: any}>},
+  onPress: (e: any) => void,
+}) {
   return (
     <View style={styles.block}>
       <TouchableWithoutFeedback onPress={props.onPress}>
@@ -144,7 +147,13 @@ type RTLSwitcherComponentState = {|
   isRTL: boolean,
 |};
 
-function withRTLState(Component) {
+function withRTLState(
+  Component: ({
+    isRTL: boolean,
+    setRTL: (isRTL: boolean) => void,
+    style?: any,
+  }) => React.Node,
+) {
   return class extends React.Component<
     {style?: any},
     RTLSwitcherComponentState,
@@ -157,7 +166,7 @@ function withRTLState(Component) {
     }
 
     render() {
-      const setRTL = isRTL => this.setState({isRTL: isRTL});
+      const setRTL = (isRTL: boolean) => this.setState({isRTL: isRTL});
       return (
         <Component isRTL={this.state.isRTL} setRTL={setRTL} {...this.props} />
       );
@@ -165,7 +174,12 @@ function withRTLState(Component) {
   };
 }
 
-const RTLToggler = ({isRTL, setRTL}) => {
+const RTLToggler = ({
+  isRTL,
+  setRTL,
+}:
+  | {isRTL: any, setRTL: any}
+  | {isRTL: boolean, setRTL: (isRTL: boolean) => void}) => {
   if (Platform.OS === 'android') {
     return <Text style={styles.rtlToggler}>{isRTL ? 'RTL' : 'LTR'}</Text>;
   }
@@ -528,7 +542,7 @@ const BorderExample = withRTLState(({isRTL, setRTL}) => {
   );
 });
 
-const directionStyle = isRTL =>
+const directionStyle = (isRTL: boolean) =>
   Platform.OS !== 'android' ? {direction: isRTL ? 'rtl' : 'ltr'} : null;
 
 const styles = StyleSheet.create({
diff --git a/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js b/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js
index ad75dac32b7..12268f6edee 100644
--- a/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js
+++ b/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js
@@ -32,7 +32,7 @@ class SafeAreaViewExample extends React.Component<
     modalVisible: false,
   };
 
-  _setModalVisible = visible => {
+  _setModalVisible = (visible: boolean) => {
     this.setState({modalVisible: visible});
   };
 
diff --git a/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js b/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js
index e86361950f2..499a077e863 100644
--- a/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js
+++ b/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js
@@ -732,7 +732,7 @@ const RefreshControlExample = () => {
     wait(2000).then(() => setRefreshing(false));
   }, []);
 
-  const wait = timeout => {
+  const wait = (timeout: number) => {
     return new Promise(resolve => {
       setTimeout(resolve, timeout);
     });
@@ -1253,7 +1253,9 @@ class Item extends React.PureComponent<{|
 
 let ITEMS = [...Array(12)].map((_, i) => `Item ${i}`);
 
-const createItemRow = (msg, index) => <Item key={index} msg={msg} />;
+const createItemRow = (msg: string, index: number) => (
+  <Item key={index} msg={msg} />
+);
 
 const Button = (props: {
   active?: boolean,
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js b/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js
index 04c5dc6ea46..498f0c4e8d9 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js
@@ -14,7 +14,8 @@ import * as React from 'react';
 export function SectionList_onEndReached(): React.Node {
   const [output, setOutput] = React.useState('');
   const exampleProps = {
-    onEndReached: info => setOutput('onEndReached'),
+    onEndReached: (info: {distanceFromEnd: number, ...}) =>
+      setOutput('onEndReached'),
     onEndReachedThreshold: 0,
   };
   const ref = React.useRef(null);
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js b/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js
index ff40342e587..f9399653088 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js
@@ -8,6 +8,7 @@
  * @flow
  */
 
+import type {ViewToken} from 'react-native/Libraries/Lists/ViewabilityHelper';
 import SectionListBaseExample from './SectionListBaseExample';
 import {View, StyleSheet, SectionList} from 'react-native';
 import * as React from 'react';
@@ -30,7 +31,11 @@ export function SectionList_onViewableItemsChanged(props: {
   const {viewabilityConfig, offScreen, horizontal, useScrollRefScroll} = props;
   const [output, setOutput] = React.useState('');
   const exampleProps = {
-    onViewableItemsChanged: info =>
+    onViewableItemsChanged: (info: {
+      changed: Array<ViewToken>,
+      viewableItems: Array<ViewToken>,
+      ...
+    }) =>
       setOutput(
         info.viewableItems
           .filter(viewToken => viewToken.index != null && viewToken.isViewable)
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js b/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js
index 88fda4e8171..58452b7badc 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {Item} from '../../components/ListExampleShared';
 const RNTesterPage = require('../../components/RNTesterPage');
 const React = require('react');
 
@@ -108,7 +109,7 @@ const EmptySectionList = () => (
 );
 
 const renderItemComponent =
-  setItemState =>
+  (setItemState: (item: Item) => void) =>
   ({item, separators}) => {
     if (isNaN(item.key)) {
       return;
@@ -164,7 +165,7 @@ export function SectionList_scrollable(Props: {
   const [data, setData] = React.useState(genItemData(1000));
 
   const filterRegex = new RegExp(String(filterText), 'i');
-  const filter = item =>
+  const filter = (item: Item) =>
     filterRegex.test(item.text) || filterRegex.test(item.title);
   const filteredData = data.filter(filter);
   const filteredSectionData = [...CONSTANT_SECTION_EXAMPLES];
@@ -181,7 +182,7 @@ export function SectionList_scrollable(Props: {
     startIndex = ii;
   }
 
-  const setItemPress = item => {
+  const setItemPress = (item: Item) => {
     if (isNaN(item.key)) {
       return;
     }
@@ -190,7 +191,7 @@ export function SectionList_scrollable(Props: {
   };
 
   const ref = React.useRef<?React.ElementRef<typeof SectionList>>(null);
-  const scrollToLocation = (sectionIndex, itemIndex) => {
+  const scrollToLocation = (sectionIndex: number, itemIndex: number) => {
     // $FlowFixMe[method-unbinding] added when improving typing for this parameters
     if (ref != null && ref.current?.scrollToLocation != null) {
       ref.current.scrollToLocation({sectionIndex, itemIndex});
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js b/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js
index ec93af1f63b..9042f205d33 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js
@@ -13,8 +13,8 @@ import {View, Text, StyleSheet} from 'react-native';
 import * as React from 'react';
 
 const Separator =
-  (defaultColor, highlightColor, isSectionSeparator) =>
-  ({leadingItem, trailingItem, highlighted, hasBeenHighlighted}) => {
+  (defaultColor: string, highlightColor: string, isSectionSeparator: boolean) =>
+  ({leadingItem, trailingItem, highlighted, hasBeenHighlighted}: any) => {
     const text = `${
       isSectionSeparator ? 'Section ' : ''
     }separator for leading ${leadingItem} and trailing ${trailingItem} has ${
diff --git a/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js b/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js
index fe7c947e909..41ff93ac454 100644
--- a/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js
+++ b/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js
@@ -8,6 +8,8 @@
  * @format
  */
 
+import type {RenderItemProps} from 'react-native/Libraries/Lists/VirtualizedList';
+
 import * as React from 'react';
 import {
   Animated,
@@ -49,7 +51,7 @@ function SwipeableCardExample() {
 
   const incrementCurrent = () => setCurrentIndex(currentIndex + 1);
 
-  const getCardColor = index => cardColors[index % cardColors.length];
+  const getCardColor = (index: number) => cardColors[index % cardColors.length];
 
   /*
    * The cards try to reuse the views. Instead of always rebuilding the current card on top
@@ -140,7 +142,7 @@ function SwipeableCard(props: {
 const cardData = Array(5);
 
 function Card(props: {color: string}) {
-  const renderItem = ({item, index}) => (
+  const renderItem = ({item, index}: RenderItemProps<$FlowFixMe>) => (
     <CardSection color={props.color} index={index} />
   );
 
diff --git a/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js b/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js
index be0a6f60357..5d27d97eccb 100644
--- a/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js
+++ b/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js
@@ -46,7 +46,7 @@ class TextInputAccessoryViewChangeTextExample extends React.Component<
   {...},
   {text: string},
 > {
-  constructor(props) {
+  constructor(props: void | {...}) {
     super(props);
     this.state = {text: 'Placeholder Text'};
   }
@@ -79,7 +79,7 @@ class TextInputAccessoryViewChangeKeyboardExample extends React.Component<
   {...},
   {keyboardType: string, text: string},
 > {
-  constructor(props) {
+  constructor(props: void | {...}) {
     super(props);
     this.state = {text: '', keyboardType: 'default'};
   }
@@ -121,7 +121,7 @@ class TextInputAccessoryViewDefaultDoneButtonExample extends React.Component<
   |}>,
   {text: string},
 > {
-  constructor(props) {
+  constructor(props: void | $ReadOnly<{keyboardType: KeyboardType}>) {
     super(props);
     this.state = {text: ''};
   }
@@ -140,7 +140,7 @@ class TextInputAccessoryViewDefaultDoneButtonExample extends React.Component<
 }
 
 class RewriteExampleKana extends React.Component<$FlowFixMeProps, any> {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -161,7 +161,7 @@ class RewriteExampleKana extends React.Component<$FlowFixMeProps, any> {
 }
 
 class SecureEntryExample extends React.Component<$FlowFixMeProps, any> {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {
       text: '',
@@ -209,7 +209,7 @@ class AutogrowingTextInputExample extends React.Component<
   $FlowFixMeProps,
   $FlowFixMeState,
 > {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
 
     this.state = {
@@ -223,7 +223,7 @@ class AutogrowingTextInputExample extends React.Component<
     };
   }
 
-  UNSAFE_componentWillReceiveProps(props) {
+  UNSAFE_componentWillReceiveProps(props: any) {
     this.setState({
       multiline: props.multiline,
     });
diff --git a/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js b/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js
index 19e758f2a7d..24874bf2dac 100644
--- a/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js
+++ b/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js
@@ -88,7 +88,7 @@ class WithLabel extends React.Component<$FlowFixMeProps> {
 }
 
 class RewriteExample extends React.Component<$FlowFixMeProps, any> {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -122,7 +122,7 @@ class RewriteExampleInvalidCharacters extends React.Component<
   $FlowFixMeProps,
   any,
 > {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -150,7 +150,7 @@ class RewriteInvalidCharactersAndClearExample extends React.Component<
 > {
   inputRef: ?React.ElementRef<typeof TextInput> = null;
 
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -248,7 +248,7 @@ class TextEventsExample extends React.Component<{...}, $FlowFixMeState> {
     prev3Text: '<No Event>',
   };
 
-  updateText = text => {
+  updateText = (text: string) => {
     this.setState(state => {
       return {
         curText: text,
@@ -305,7 +305,7 @@ class TokenizedTextExample extends React.Component<
   $FlowFixMeProps,
   $FlowFixMeState,
 > {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: 'Hello #World'};
   }
@@ -396,7 +396,7 @@ class SelectionExample extends React.Component<
     return Math.round(Math.random() * length);
   }
 
-  select(start, end) {
+  select(start: number, end: number) {
     this._textInput?.focus();
     this.setState({selection: {start, end}});
     if (this.props.imperative) {
@@ -412,7 +412,7 @@ class SelectionExample extends React.Component<
     this.select(...positions);
   }
 
-  placeAt(position) {
+  placeAt(position: number) {
     this.select(position, position);
   }
 
diff --git a/packages/rn-tester/js/examples/Timer/TimerExample.js b/packages/rn-tester/js/examples/Timer/TimerExample.js
index e06b1cd227f..2a4b75849fc 100644
--- a/packages/rn-tester/js/examples/Timer/TimerExample.js
+++ b/packages/rn-tester/js/examples/Timer/TimerExample.js
@@ -15,7 +15,7 @@ const React = require('react');
 
 const {Alert, Platform, ToastAndroid, Text, View} = require('react-native');
 
-function burnCPU(milliseconds) {
+function burnCPU(milliseconds: number) {
   const start = global.performance.now();
   while (global.performance.now() < start + milliseconds) {}
 }
@@ -117,7 +117,11 @@ class RequestIdleCallbackTester extends React.Component<
       this._idleTimer = null;
     }
 
-    const handler = deadline => {
+    const handler = (deadline: {
+      didTimeout: boolean,
+      timeRemaining: () => number,
+      ...
+    }) => {
       while (deadline.timeRemaining() > 5) {
         burnCPU(5);
         this.setState({
diff --git a/packages/rn-tester/js/examples/Touchable/TouchableExample.js b/packages/rn-tester/js/examples/Touchable/TouchableExample.js
index eed3b4a53a2..a4df8b52ada 100644
--- a/packages/rn-tester/js/examples/Touchable/TouchableExample.js
+++ b/packages/rn-tester/js/examples/Touchable/TouchableExample.js
@@ -181,7 +181,7 @@ class TouchableFeedbackEvents extends React.Component<{...}, $FlowFixMeState> {
     );
   }
 
-  _appendEvent = eventName => {
+  _appendEvent = (eventName: string) => {
     const limit = 6;
     const eventLog = this.state.eventLog.slice(0, limit - 1);
     eventLog.unshift(eventName);
@@ -222,7 +222,7 @@ class TouchableDelayEvents extends React.Component<{...}, $FlowFixMeState> {
     );
   }
 
-  _appendEvent = eventName => {
+  _appendEvent = (eventName: string) => {
     const limit = 6;
     const eventLog = this.state.eventLog.slice(0, limit - 1);
     eventLog.unshift(eventName);
diff --git a/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js b/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js
index 96c91a34f11..09e14a94e24 100644
--- a/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js
+++ b/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js
@@ -73,7 +73,33 @@ class SampleTurboModuleExample extends React.Component<{||}, State> {
       NativeSampleTurboModule.getValue(5, 'test', {a: 1, b: 'foo'}),
   };
 
-  _setResult(name, result) {
+  _setResult(
+    name:
+      | string
+      | 'callback'
+      | 'getArray'
+      | 'getBool'
+      | 'getConstants'
+      | 'getNumber'
+      | 'getObject'
+      | 'getRootTag'
+      | 'getString'
+      | 'getUnsafeObject'
+      | 'getValue'
+      | 'promise'
+      | 'rejectPromise'
+      | 'voidFunc',
+    result:
+      | $FlowFixMe
+      | void
+      | RootTag
+      | Promise<mixed>
+      | number
+      | string
+      | boolean
+      | {const1: boolean, const2: number, const3: string}
+      | Array<$FlowFixMe>,
+  ) {
     this.setState(({testResults}) => ({
       /* $FlowFixMe[cannot-spread-indexer] (>=0.122.0 site=react_native_fb)
        * This comment suppresses an error found when Flow v0.122.0 was
@@ -88,7 +114,22 @@ class SampleTurboModuleExample extends React.Component<{||}, State> {
     }));
   }
 
-  _renderResult(name) {
+  _renderResult(
+    name:
+      | 'callback'
+      | 'getArray'
+      | 'getBool'
+      | 'getConstants'
+      | 'getNumber'
+      | 'getObject'
+      | 'getRootTag'
+      | 'getString'
+      | 'getUnsafeObject'
+      | 'getValue'
+      | 'promise'
+      | 'rejectPromise'
+      | 'voidFunc',
+  ) {
     const result = this.state.testResults[name] || {};
     return (
       <View style={styles.result}>