facebook · panagosg7 · May 22, 2025
diff --git a/packages/react-native-babel-transformer/src/index.js b/packages/react-native-babel-transformer/src/index.js
@@ -188,7 +188,7 @@ const transform /*: BabelTransformer['transform'] */ = ({
     : process.env.BABEL_ENV || 'production';
 
   try {
-    const babelConfig = {
+    const babelConfig /*: BabelCoreOptions */ = {
       // ES modules require sourceType='module' but OSS may not always want that
       sourceType: 'unambiguous',
       ...buildBabelConfig(filename, options, plugins),

diff --git a/packages/react-native-compatibility-check/src/VersionDiffing.js b/packages/react-native-compatibility-check/src/VersionDiffing.js
@@ -976,14 +976,14 @@ function buildNativeModulesDiff(
     objectTypeChanges,
   );
 
-  const newType = {
+  const newType: CompleteTypeAnnotation = {
     type: 'ObjectTypeAnnotation',
     properties: [
       ...newerNativeModule.spec.methods,
       ...newerNativeModule.spec.eventEmitters,
     ],
   };
-  const oldType = {
+  const oldType: CompleteTypeAnnotation = {
     type: 'ObjectTypeAnnotation',
     properties: [
       ...olderNativeModule.spec.methods,
@@ -1073,11 +1073,11 @@ function buildNativeComponentsDiff(
           olderCommand => olderCommand.name === command.name,
         );
 
-        const newCommands = {
+        const newCommands: CompleteTypeAnnotation = {
           type: 'ObjectTypeAnnotation',
           properties: [command],
         };
-        const oldCommands =
+        const oldCommands: ?CompleteTypeAnnotation =
           oldCommand != null
             ? {
                 type: 'ObjectTypeAnnotation',
@@ -1123,15 +1123,15 @@ function buildNativeComponentsDiff(
 
       // We have to do this to remove the .defaults from the props and get it into
       // standard JavaScript shapes.
-      const newConvertedProps = {
+      const newConvertedProps: CompleteTypeAnnotation = {
         type: 'ObjectTypeAnnotation',
         properties: newerComponent.props.map(prop => ({
           name: prop.name,
           optional: prop.optional,
           typeAnnotation: convertPropToBasicTypes(prop.typeAnnotation),
         })),
       };
-      const oldConvertedProps = {
+      const oldConvertedProps: CompleteTypeAnnotation = {
         type: 'ObjectTypeAnnotation',
         properties: olderComponent.props.map(prop => ({
           name: prop.name,

diff --git a/packages/react-native-fantom/runner/runner.js b/packages/react-native-fantom/runner/runner.js
@@ -9,7 +9,11 @@
  */
 
 import type {TestSuiteResult} from '../runtime/setup';
-import type {AsyncCommandResult, HermesVariant} from './utils';
+import type {
+  AsyncCommandResult,
+  ConsoleLogMessage,
+  HermesVariant,
+} from './utils';
 
 import entrypointTemplate from './entrypoint-template';
 import * as EnvironmentOptions from './EnvironmentOptions';
@@ -69,7 +73,7 @@ async function processRNTesterCommandResult(
       return;
     }
 
-    let parsed;
+    let parsed: ConsoleLogMessage;
     try {
       parsed = JSON.parse(line);
     } catch {

diff --git a/packages/react-native-fantom/runtime/setup.js b/packages/react-native-fantom/runtime/setup.js
@@ -320,7 +320,7 @@ function runSpec(spec: Spec): TestCaseResult {
     return result;
   }
 
-  let status;
+  let status: 'passed' | 'failed' | 'pending';
   let error;
 
   const start = Date.now();

diff --git a/packages/react-native/Libraries/Components/DrawerAndroid/DrawerLayoutAndroid.android.js b/packages/react-native/Libraries/Components/DrawerAndroid/DrawerLayoutAndroid.android.js
@@ -30,7 +30,7 @@ import nullthrows from 'nullthrows';
 import * as React from 'react';
 import {createRef} from 'react';
 
-const DRAWER_STATES = ['Idle', 'Dragging', 'Settling'];
+const DRAWER_STATES = ['Idle', 'Dragging', 'Settling'] as const;
 
 /**
  * React component that wraps the platform `DrawerLayout` (Android only). The

diff --git a/packages/react-native/Libraries/Components/ScrollView/ScrollView.js b/packages/react-native/Libraries/Components/ScrollView/ScrollView.js
@@ -1646,7 +1646,9 @@ class ScrollView extends React.Component<ScrollViewProps, ScrollViewState> {
     if (__DEV__ && this.props.style !== undefined) {
       // $FlowFixMe[underconstrained-implicit-instantiation]
       const style = flattenStyle(this.props.style);
-      const childLayoutProps = ['alignItems', 'justifyContent'].filter(
+      const childLayoutProps = (
+        ['alignItems', 'justifyContent'] as const
+      ).filter(
         // $FlowFixMe[incompatible-use]
         prop => style && style[prop] !== undefined,
       );

diff --git a/packages/react-native/Libraries/Components/Touchable/TouchableWithoutFeedback.js b/packages/react-native/Libraries/Components/Touchable/TouchableWithoutFeedback.js
@@ -152,7 +152,7 @@ const PASSTHROUGH_PROPS = [
   'onFocus',
   'onLayout',
   'testID',
-];
+] as const;
 
 /**
  * Do not use unless you have a very good reason.

diff --git a/packages/react-native/Libraries/Core/setUpDeveloperTools.js b/packages/react-native/Libraries/Core/setUpDeveloperTools.js
@@ -23,17 +23,19 @@ if (__DEV__) {
     // TODO(T214991636): Remove legacy Metro log forwarding
     if (console._isPolyfilled) {
       // We assume full control over the console and send JavaScript logs to Metro.
-      [
-        'trace',
-        'info',
-        'warn',
-        'error',
-        'log',
-        'group',
-        'groupCollapsed',
-        'groupEnd',
-        'debug',
-      ].forEach(level => {
+      (
+        [
+          'trace',
+          'info',
+          'warn',
+          'error',
+          'log',
+          'group',
+          'groupCollapsed',
+          'groupEnd',
+          'debug',
+        ] as const
+      ).forEach(level => {
         const originalFunction = console[level];
         console[level] = function (...args: $ReadOnlyArray<mixed>) {
           HMRClient.log(level, args);

diff --git a/packages/react-native/Libraries/Text/Text.js b/packages/react-native/Libraries/Text/Text.js
@@ -545,6 +545,6 @@ const verticalAlignToTextAlignVerticalMap = {
   top: 'top',
   bottom: 'bottom',
   middle: 'center',
-};
+} as const;
 
 export default TextImpl;
diff --git a/packages/react-native/scripts/ios-prebuild/hermes.js b/packages/react-native/scripts/ios-prebuild/hermes.js
@@ -97,10 +97,10 @@ type HermesEngineSourceType =
 */
 
 const HermesEngineSourceTypes = {
-  LOCAL_PREBUILT_TARBALL: 'local_prebuilt_tarball',
-  DOWNLOAD_PREBUILD_TARBALL: 'download_prebuild_tarball',
-  DOWNLOAD_PREBUILT_NIGHTLY_TARBALL: 'download_prebuilt_nightly_tarball',
-};
+    LOCAL_PREBUILT_TARBALL: 'local_prebuilt_tarball',
+    DOWNLOAD_PREBUILD_TARBALL: 'download_prebuild_tarball',
+    DOWNLOAD_PREBUILT_NIGHTLY_TARBALL: 'download_prebuilt_nightly_tarball',
+  } /*:: as const */;
 
 /**
  * Checks if the Hermes artifacts are already downloaded and up to date with the specified version.

diff --git a/packages/react-native/src/private/animated/__tests__/createAnimatedPropsMemoHook-test.js b/packages/react-native/src/private/animated/__tests__/createAnimatedPropsMemoHook-test.js
@@ -20,11 +20,11 @@ describe('createCompositeKeyForProps', () => {
     it('excludes non-array and non-object allowlisted props', () => {
       const props = {string: 'abc', number: 123, boolean: true, function() {}};
       const allowlist = {
-        string: true,
-        number: true,
-        boolean: true,
-        function: true,
-      };
+          string: true,
+          number: true,
+          boolean: true,
+          function: true,
+        } /*:: as const */;
       const compositeKey = createCompositeKeyForProps(props, allowlist);
 
       expect(compositeKey).toEqual(null);
@@ -53,8 +53,8 @@ describe('createCompositeKeyForProps', () => {
         bar: new AnimatedEvent([], {useNativeDriver: true}),
       };
       const allowlist = {
-        bar: true,
-      };
+          bar: true,
+        } /*:: as const */;
       const compositeKey = createCompositeKeyForProps(props, allowlist);
 
       expect(compositeKey).toEqual({bar: props.bar});
@@ -69,10 +69,10 @@ describe('createCompositeKeyForProps', () => {
         },
       };
       const allowlist = {
-        style: {
-          baz: true,
-        },
-      };
+          style: {
+            baz: true,
+          },
+        } /*:: as const */;
       const compositeKey = createCompositeKeyForProps(props, allowlist);
 
       expect(compositeKey).toEqual(null);
@@ -84,8 +84,8 @@ describe('createCompositeKeyForProps', () => {
         bar: new AnimatedValue(1),
       };
       const allowlist = {
-        bar: true,
-      };
+          bar: true,
+        } /*:: as const */;
       const compositeKey = createCompositeKeyForProps(props, allowlist);
 
       expect(compositeKey).toEqual({bar: props.bar});
@@ -108,7 +108,7 @@ describe('createCompositeKeyForProps', () => {
       const props = {
         style: {opacity, transform: [{rotateX: 1}, {rotateY}, {rotateZ: 1}]},
       };
-      const allowlist = {style: {transform: true}};
+      const allowlist = {style: {transform: true}} /*:: as const */;
       const compositeKey = createCompositeKeyForProps(props, allowlist);
 
       expect(compositeKey).toEqual({
@@ -126,7 +126,7 @@ describe('createCompositeKeyForProps', () => {
       const props = {
         style: [{opacity: opacityA}, {opacity: opacityB}],
       };
-      const allowlist = {style: {opacity: true}};
+      const allowlist = {style: {opacity: true}} /*:: as const */;
       const compositeKey = createCompositeKeyForProps(props, allowlist);
 
       expect(compositeKey).toEqual({style: {opacity: opacityB}});

diff --git a/packages/rn-tester/IntegrationTests/ImageCachePolicyTest.js b/packages/rn-tester/IntegrationTests/ImageCachePolicyTest.js
@@ -28,7 +28,7 @@ const {TestModule} = NativeModules;
  * image with the new one and make sure they are the same.
  */
 
-const TESTS = ['only-if-cached', 'default', 'reload', 'force-cache'];
+const TESTS = ['only-if-cached', 'default', 'reload', 'force-cache'] as const;
 
 function ImageCachePolicyTest(): React.Node {
   const [state, setState] = useState({

diff --git a/packages/rn-tester/js/examples/Accessibility/AccessibilityAndroidExample.js b/packages/rn-tester/js/examples/Accessibility/AccessibilityAndroidExample.js
@@ -21,7 +21,7 @@ const importantForAccessibilityValues = [
   'yes',
   'no',
   'no-hide-descendants',
-];
+] as const;
 
 type AccessibilityAndroidExampleState = {
   count: number,

diff --git a/packages/rn-tester/js/examples/MixBlendMode/MixBlendModeExample.js b/packages/rn-tester/js/examples/MixBlendMode/MixBlendModeExample.js
@@ -131,7 +131,7 @@ const mixBlendModes = [
   'saturation',
   'color',
   'luminosity',
-];
+] as const;
 
 const examples: Array<RNTesterModuleExample> = mixBlendModes.map(mode => ({
   title: mode,

diff --git a/packages/rn-tester/js/examples/Modal/ModalPresentation.js b/packages/rn-tester/js/examples/Modal/ModalPresentation.js
@@ -21,20 +21,20 @@ import * as React from 'react';
 import {useCallback, useContext, useState} from 'react';
 import {Modal, Platform, StyleSheet, Switch, Text, View} from 'react-native';
 
-const animationTypes = ['slide', 'none', 'fade'];
+const animationTypes = ['slide', 'none', 'fade'] as const;
 const presentationStyles = [
   'fullScreen',
   'pageSheet',
   'formSheet',
   'overFullScreen',
-];
+] as const;
 const supportedOrientations = [
   'portrait',
   'portrait-upside-down',
   'landscape',
   'landscape-left',
   'landscape-right',
-];
+] as const;
 
 const backdropColors = ['red', 'blue', undefined];
 

diff --git a/packages/rn-tester/js/examples/Text/TextExample.ios.js b/packages/rn-tester/js/examples/Text/TextExample.ios.js
@@ -1438,7 +1438,12 @@ const examples = [
   {
     title: 'Line Break Strategy',
     render: function (): React.Node {
-      const lineBreakStrategy = ['none', 'standard', 'hangul-word', 'push-out'];
+      const lineBreakStrategy = [
+        'none',
+        'standard',
+        'hangul-word',
+        'push-out',
+      ] as const;
       const textByCode = {
         en: 'lineBreakStrategy lineBreakStrategy lineBreakStrategy lineBreakStrategy',
         ko: '한글개행 한글개행 한글개행 한글개행 한글개행 한글개행 한글개행 한글개행',

diff --git a/packages/rn-tester/js/examples/TextInput/TextInputExample.android.js b/packages/rn-tester/js/examples/TextInput/TextInputExample.android.js
@@ -119,19 +119,21 @@ const examples: Array<RNTesterModuleExample> = [
             defaultValue="Font Weight (default)"
             style={[styles.singleLine]}
           />
-          {[
-            'normal',
-            'bold',
-            '900',
-            800,
-            '700',
-            '600',
-            '500',
-            '400',
-            '300',
-            '200',
-            '100',
-          ].map(fontWeight => (
+          {(
+            [
+              'normal',
+              'bold',
+              '900',
+              800,
+              '700',
+              '600',
+              '500',
+              '400',
+              '300',
+              '200',
+              '100',
+            ] as const
+          ).map(fontWeight => (
             <ExampleTextInput
               defaultValue={`Font Weight (${fontWeight})`}
               key={fontWeight}
@@ -389,7 +391,7 @@ const examples: Array<RNTesterModuleExample> = [
         'done',
         'previous',
         'next',
-      ];
+      ] as const;
       const returnKeyLabels = ['Compile', 'React Native'];
       const returnKeyExamples = returnKeyTypes.map(type => {
         return (