diff --git a/Libraries/Animated/useAnimatedProps.js b/Libraries/Animated/useAnimatedProps.js
index d7329a7e606..137a8de6200 100644
--- a/Libraries/Animated/useAnimatedProps.js
+++ b/Libraries/Animated/useAnimatedProps.js
@@ -60,7 +60,7 @@ export default function useAnimatedProps<TProps: {...}, TInstance>(
   // But there is no way to transparently compose three separate callback refs,
   // so we just combine them all into one for now.
   const refEffect = useCallback(
-    instance => {
+    (instance: TInstance) => {
       // NOTE: This may be called more often than necessary (e.g. when `props`
       // changes), but `setNativeView` already optimizes for that.
       node.setNativeView(instance);
diff --git a/Libraries/Utilities/useRefEffect.js b/Libraries/Utilities/useRefEffect.js
index b79a644b83c..26446cbf536 100644
--- a/Libraries/Utilities/useRefEffect.js
+++ b/Libraries/Utilities/useRefEffect.js
@@ -31,7 +31,7 @@ export default function useRefEffect<TInstance>(
 ): CallbackRef<TInstance | null> {
   const cleanupRef = useRef<(() => void) | void>(undefined);
   return useCallback(
-    instance => {
+    (instance: null | TInstance) => {
       if (cleanupRef.current) {
         cleanupRef.current();
         cleanupRef.current = undefined;
diff --git a/packages/rn-tester/js/RNTesterAppShared.js b/packages/rn-tester/js/RNTesterAppShared.js
index fc35f5c89f5..49094edf4c2 100644
--- a/packages/rn-tester/js/RNTesterAppShared.js
+++ b/packages/rn-tester/js/RNTesterAppShared.js
@@ -111,7 +111,7 @@ const RNTesterApp = (): React.Node => {
   );
 
   const handleModuleExampleCardPress = React.useCallback(
-    exampleName => {
+    (exampleName: string) => {
       dispatch({
         type: RNTesterActionsType.EXAMPLE_CARD_PRESS,
         data: {key: exampleName},
@@ -131,7 +131,7 @@ const RNTesterApp = (): React.Node => {
   );
 
   const handleNavBarPress = React.useCallback(
-    args => {
+    (args: {screen: string}) => {
       dispatch({
         type: RNTesterActionsType.NAVBAR_PRESS,
         data: {screen: args.screen},
diff --git a/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js b/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
index 8cdc2d04915..3a9540468ea 100644
--- a/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
+++ b/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
@@ -68,7 +68,7 @@ function FilterModalButton(props: FilterModalProps) {
     setModalVisible(false);
   }, []);
 
-  const onPendingTextChange = useCallback(newText => {
+  const onPendingTextChange = useCallback((newText: string) => {
     setPendingFilterText(newText);
   }, []);
 
diff --git a/packages/rn-tester/js/examples/Experimental/PlatformTest/usePlatformTestHarness.js b/packages/rn-tester/js/examples/Experimental/PlatformTest/usePlatformTestHarness.js
index 967c336baae..8c55230414e 100644
--- a/packages/rn-tester/js/examples/Experimental/PlatformTest/usePlatformTestHarness.js
+++ b/packages/rn-tester/js/examples/Experimental/PlatformTest/usePlatformTestHarness.js
@@ -106,7 +106,7 @@ function constructAsyncTestHook(
       });
     }, [description]);
 
-    const stepHandler = useCallback(testCase => {
+    const stepHandler = useCallback((testCase: PlatformTestCase) => {
       const stepAssertions = runTestCase(testCase);
       assertionsRef.current.push(...stepAssertions);
     }, []);
diff --git a/packages/rn-tester/js/examples/FlatList/FlatList-nested.js b/packages/rn-tester/js/examples/FlatList/FlatList-nested.js
index b2b1689d2db..f2d1282a5a7 100644
--- a/packages/rn-tester/js/examples/FlatList/FlatList-nested.js
+++ b/packages/rn-tester/js/examples/FlatList/FlatList-nested.js
@@ -16,6 +16,7 @@ import {FlatList, StyleSheet, Text, View} from 'react-native';
 
 import RNTesterPage from '../../components/RNTesterPage';
 import type {RNTesterModuleExample} from '../../types/RNTesterTypes';
+import type {ViewToken} from '../../../../../Libraries/Lists/ViewabilityHelper';
 
 type OuterItem = 'head' | 'vertical' | 'horizontal' | 'filler';
 
@@ -78,7 +79,13 @@ function NestedListExample(): React.Node {
   const [inner, dispatchInner] = useReducer(reducer, initialItemsState);
 
   const onViewableItemsChanged = useCallback(
-    ({changed}) => {
+    ({
+      changed,
+    }: {
+      changed: Array<ViewToken>,
+      viewableItems: Array<ViewToken>,
+      ...
+    }) => {
       for (const token of changed) {
         dispatchOuter({
           type: token.isViewable ? 'add-viewable' : 'remove-viewable',
@@ -162,7 +169,13 @@ function OuterItemRenderer({
   }, [dispatchOuter, index]);
 
   const onViewableItemsChanged = useCallback(
-    ({changed}) => {
+    ({
+      changed,
+    }: {
+      changed: Array<ViewToken>,
+      viewableItems: Array<ViewToken>,
+      ...
+    }) => {
       for (const token of changed) {
         dispatchInner({
           type: token.isViewable ? 'add-viewable' : 'remove-viewable',
diff --git a/packages/rn-tester/js/examples/FlatList/FlatList-onViewableItemsChanged.js b/packages/rn-tester/js/examples/FlatList/FlatList-onViewableItemsChanged.js
index 8f35338ccb1..981d226dc1e 100644
--- a/packages/rn-tester/js/examples/FlatList/FlatList-onViewableItemsChanged.js
+++ b/packages/rn-tester/js/examples/FlatList/FlatList-onViewableItemsChanged.js
@@ -9,7 +9,9 @@
  */
 
 'use strict';
+
 import type {RNTesterModuleExample} from '../../types/RNTesterTypes';
+import type {ViewToken} from '../../../../../Libraries/Lists/ViewabilityHelper';
 import BaseFlatListExample from './BaseFlatListExample';
 import {StyleSheet, View, FlatList} from 'react-native';
 import * as React from 'react';
@@ -32,7 +34,7 @@ export function FlatList_onViewableItemsChanged(props: {
   const {viewabilityConfig, offScreen, horizontal, useScrollRefScroll} = props;
   const [output, setOutput] = React.useState('');
   const onViewableItemsChanged = React.useCallback(
-    info =>
+    (info: {changed: Array<ViewToken>, viewableItems: Array<ViewToken>, ...}) =>
       setOutput(
         info.viewableItems
           .filter(viewToken => viewToken.index != null && viewToken.isViewable)