facebook · kassens · Aug 22, 2025 · Aug 20, 2025
diff --git a/.eslintrc.js b/.eslintrc.js
@@ -565,6 +565,7 @@ module.exports = {
     BigInt: 'readonly',
     BigInt64Array: 'readonly',
     BigUint64Array: 'readonly',
+    CacheType: 'readonly',
     Class: 'readonly',
     ClientRect: 'readonly',
     CopyInspectedElementPath: 'readonly',

diff --git a/package.json b/package.json
@@ -74,8 +74,8 @@
     "eslint-plugin-react-internal": "link:./scripts/eslint-rules",
     "fbjs-scripts": "^3.0.1",
     "filesize": "^6.0.1",
-    "flow-bin": "^0.272",
-    "flow-remove-types": "^2.272",
+    "flow-bin": "^0.273",
+    "flow-remove-types": "^2.273",
     "flow-typed": "^4.1.1",
     "glob": "^7.1.6",
     "glob-stream": "^6.1.0",

diff --git a/packages/react-devtools-shared/src/backend/fiber/renderer.js b/packages/react-devtools-shared/src/backend/fiber/renderer.js
@@ -6705,7 +6705,7 @@ export function attach(
     if (isMostRecentlyInspectedElement(id) && !forceFullData) {
       if (!hasElementUpdatedSinceLastInspected) {
         if (path !== null) {
-          let secondaryCategory = null;
+          let secondaryCategory: 'suspendedBy' | 'hooks' | null = null;
           if (path[0] === 'hooks') {
             secondaryCategory = 'hooks';
           }

diff --git a/packages/react-devtools-shared/src/hookNamesCache.js b/packages/react-devtools-shared/src/hookNamesCache.js
@@ -103,7 +103,7 @@ export function loadHookNames(
 
     let timeoutID: $FlowFixMe | null;
     let didTimeout = false;
-    let status = 'unknown';
+    let status: 'success' | 'error' | 'timeout' | 'unknown' = 'unknown';
     let resolvedHookNames: HookNames | null = null;
 
     const wake = () => {

diff --git a/packages/react-devtools-shared/src/hooks/parseHookNames/loadSourceAndMetadata.js b/packages/react-devtools-shared/src/hooks/parseHookNames/loadSourceAndMetadata.js
@@ -64,7 +64,7 @@ import type {FetchFileWithCaching} from 'react-devtools-shared/src/devtools/view
 
 // Prefer a cached albeit stale response to reduce download time.
 // We wouldn't want to load/parse a newer version of the source (even if one existed).
-const FETCH_OPTIONS = {cache: 'force-cache'};
+const FETCH_OPTIONS = {cache: 'force-cache' as CacheType};
 
 const MAX_SOURCE_LENGTH = 100_000_000;
 

diff --git a/packages/react-devtools-timeline/src/import-worker/preprocessData.js b/packages/react-devtools-timeline/src/import-worker/preprocessData.js
@@ -509,7 +509,7 @@ function processTimelineEvent(
       } else if (name.startsWith('--schedule-forced-update-')) {
         const [laneBitmaskString, componentName] = name.slice(25).split('-');
 
-        const forceUpdateEvent = {
+        const forceUpdateEvent: SchedulingEvent = {
           type: 'schedule-force-update',
           lanes: getLanesFromTransportDecimalBitmask(laneBitmaskString),
           componentName,
@@ -527,7 +527,7 @@ function processTimelineEvent(
       } else if (name.startsWith('--schedule-state-update-')) {
         const [laneBitmaskString, componentName] = name.slice(24).split('-');
 
-        const stateUpdateEvent = {
+        const stateUpdateEvent: SchedulingEvent = {
           type: 'schedule-state-update',
           lanes: getLanesFromTransportDecimalBitmask(laneBitmaskString),
           componentName,
@@ -578,7 +578,7 @@ function processTimelineEvent(
         // We can't know if they'll be resolved or not at this point.
         // We'll just give them a default (fake) duration width.
 
-        const suspenseEvent = {
+        const suspenseEvent: SuspenseEvent = {
           componentName,
           depth,
           duration: null,

diff --git a/packages/react-dom-bindings/src/client/inputValueTracking.js b/packages/react-dom-bindings/src/client/inputValueTracking.js
@@ -140,7 +140,7 @@ export function trackHydrated(
     return false;
   }
 
-  let valueField;
+  let valueField: 'checked' | 'value';
   let expectedValue;
   if (isCheckable(node)) {
     valueField = 'checked';
@@ -150,8 +150,11 @@ export function trackHydrated(
     valueField = 'value';
     expectedValue = initialValue;
   }
-  // eslint-disable-next-line react-internal/safe-string-coercion
-  const currentValue = '' + (node[valueField]: any);
+  const currentValue =
+    // eslint-disable-next-line react-internal/safe-string-coercion
+    '' +
+    (// $FlowFixMe[prop-missing]
+    node[valueField]: any);
   node._valueTracker = trackValueOnNode(node, valueField, expectedValue);
   return currentValue !== expectedValue;
 }

diff --git a/packages/react-dom-bindings/src/events/SyntheticEvent.js b/packages/react-dom-bindings/src/events/SyntheticEvent.js
@@ -146,7 +146,7 @@ function createSyntheticEvent(Interface: EventInterfaceType) {
  * @interface Event
  * @see http://www.w3.org/TR/DOM-Level-3-Events/
  */
-const EventInterface = {
+const EventInterface: EventInterfaceType = {
   eventPhase: 0,
   bubbles: 0,
   cancelable: 0,
@@ -442,7 +442,7 @@ function getEventModifierState(nativeEvent: {[propName: string]: mixed}) {
  * @interface KeyboardEvent
  * @see http://www.w3.org/TR/DOM-Level-3-Events/
  */
-const KeyboardEventInterface = {
+const KeyboardEventInterface: EventInterfaceType = {
   ...UIEventInterface,
   key: getEventKey,
   code: 0,
@@ -505,7 +505,7 @@ export const SyntheticKeyboardEvent: $FlowFixMe = createSyntheticEvent(
  * @interface PointerEvent
  * @see http://www.w3.org/TR/pointerevents/
  */
-const PointerEventInterface = {
+const PointerEventInterface: EventInterfaceType = {
   ...MouseEventInterface,
   pointerId: 0,
   width: 0,
@@ -526,7 +526,7 @@ export const SyntheticPointerEvent: $FlowFixMe = createSyntheticEvent(
  * @interface TouchEvent
  * @see http://www.w3.org/TR/touch-events/
  */
-const TouchEventInterface = {
+const TouchEventInterface: EventInterfaceType = {
   ...UIEventInterface,
   touches: 0,
   targetTouches: 0,
@@ -545,7 +545,7 @@ export const SyntheticTouchEvent: $FlowFixMe =
  * @see http://www.w3.org/TR/2009/WD-css3-transitions-20090320/#transition-events-
  * @see https://developer.mozilla.org/en-US/docs/Web/API/TransitionEvent
  */
-const TransitionEventInterface = {
+const TransitionEventInterface: EventInterfaceType = {
   ...EventInterface,
   propertyName: 0,
   elapsedTime: 0,
@@ -559,7 +559,7 @@ export const SyntheticTransitionEvent: $FlowFixMe = createSyntheticEvent(
  * @interface WheelEvent
  * @see http://www.w3.org/TR/DOM-Level-3-Events/
  */
-const WheelEventInterface = {
+const WheelEventInterface: EventInterfaceType = {
   ...MouseEventInterface,
   deltaX(event: {[propName: string]: mixed}) {
     return 'deltaX' in event
@@ -594,7 +594,7 @@ const WheelEventInterface = {
 export const SyntheticWheelEvent: $FlowFixMe =
   createSyntheticEvent(WheelEventInterface);
 
-const ToggleEventInterface = {
+const ToggleEventInterface: EventInterfaceType = {
   ...EventInterface,
   newState: 0,
   oldState: 0,

diff --git a/packages/react-dom-bindings/src/shared/ReactDOMFormActions.js b/packages/react-dom-bindings/src/shared/ReactDOMFormActions.js
@@ -31,7 +31,7 @@ export type FormStatus = FormStatusPending | FormStatusNotPending;
 
 // Since the "not pending" value is always the same, we can reuse the
 // same object across all transitions.
-const sharedNotPendingObject = {
+const sharedNotPendingObject: FormStatusNotPending = {
   pending: false,
   data: null,
   method: null,

diff --git a/packages/react-native-renderer/src/legacy-events/ResponderTouchHistoryStore.js b/packages/react-native-renderer/src/legacy-events/ResponderTouchHistoryStore.js
@@ -207,6 +207,7 @@ const ResponderTouchHistoryStore = {
       touchHistory.numberActiveTouches = nativeEvent.touches.length;
       if (touchHistory.numberActiveTouches === 1) {
         touchHistory.indexOfSingleActiveTouch =
+          // $FlowFixMe[incompatible-type] might be null according to type
           nativeEvent.touches[0].identifier;
       }
     } else if (isEndish(topLevelType)) {

diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.js b/packages/react-reconciler/src/ReactFiberCommitWork.js
@@ -5020,7 +5020,7 @@ function commitPassiveUnmountInsideDeletedTreeOnFiber(
         const instance: OffscreenInstance = offscreenFiber.stateNode;
         const transitions = instance._transitions;
         if (transitions !== null) {
-          const abortReason = {
+          const abortReason: TransitionAbort = {
             reason: 'suspense',
             name: current.memoizedProps.name || null,
           };
@@ -5061,7 +5061,7 @@ function commitPassiveUnmountInsideDeletedTreeOnFiber(
         const instance: TracingMarkerInstance = current.stateNode;
         const transitions = instance.transitions;
         if (transitions !== null) {
-          const abortReason = {
+          const abortReason: TransitionAbort = {
             reason: 'marker',
             name: current.memoizedProps.name,
           };

diff --git a/packages/react-test-renderer/src/ReactTestRenderer.js b/packages/react-test-renderer/src/ReactTestRenderer.js
@@ -9,6 +9,7 @@
 
 import type {Fiber, FiberRoot} from 'react-reconciler/src/ReactInternalTypes';
 import type {
+  Container,
   PublicInstance,
   Instance,
   TextInstance,
@@ -505,7 +506,7 @@ function create(
       isStrictMode = true;
     }
   }
-  let container = {
+  let container: Container = {
     children: ([]: Array<Instance | TextInstance>),
     createNodeMock,
     tag: 'CONTAINER',

diff --git a/packages/scheduler/src/forks/SchedulerPostTask.js b/packages/scheduler/src/forks/SchedulerPostTask.js
@@ -76,7 +76,7 @@ export function unstable_scheduleCallback<T>(
   callback: SchedulerCallback<T>,
   options?: {delay?: number},
 ): CallbackNode {
-  let postTaskPriority;
+  let postTaskPriority: PostTaskPriorityLevel;
   switch (priorityLevel) {
     case ImmediatePriority:
     case UserBlockingPriority:

diff --git a/packages/use-sync-external-store/src/useSyncExternalStoreWithSelector.js b/packages/use-sync-external-store/src/useSyncExternalStoreWithSelector.js
@@ -23,19 +23,19 @@ export function useSyncExternalStoreWithSelector<Snapshot, Selection>(
   selector: (snapshot: Snapshot) => Selection,
   isEqual?: (a: Selection, b: Selection) => boolean,
 ): Selection {
-  // Use this to track the rendered snapshot.
-  const instRef = useRef<
+  type Inst =
     | {
         hasValue: true,
         value: Selection,
       }
     | {
         hasValue: false,
         value: null,
-      }
-    | null,
-  >(null);
-  let inst;
+      };
+
+  // Use this to track the rendered snapshot.
+  const instRef = useRef<Inst | null>(null);
+  let inst: Inst;
   if (instRef.current === null) {
     inst = {
       hasValue: false,

diff --git a/yarn.lock b/yarn.lock
@@ -9298,12 +9298,12 @@ flatted@^3.2.9:
   resolved "https://registry.yarnpkg.com/flatted/-/flatted-3.3.1.tgz#21db470729a6734d4997002f439cb308987f567a"
   integrity sha512-X8cqMLLie7KsNUDSdzeN8FYK9rEt4Dt67OsG/DNGnYTSDBG4uFAJFBnUeiV+zCVAvwFy56IjM9sH51jVaEhNxw==
 
-flow-bin@^0.272:
-  version "0.272.2"
-  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.272.2.tgz#918fc58dc7a99725a83314f453d3e49a56aebdc5"
-  integrity sha512-Rf8UG1biRBUGGh6qN7Ua2Y2lJRpR8Pbzby5kfHQ5m5SgjC5eOPw3Qjbrheb9ec5oU4L1gCOXRYbkbpr02PRUBw==
+flow-bin@^0.273:
+  version "0.273.1"
+  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.273.1.tgz#18621f169ecbabe3656c56980ebaabc439ee76c1"
+  integrity sha512-OlJkNCSd+i6z5xDoyGiS+3X5xYQx+vVUY2iUw6cHJR0LK3ttyA1wkiI93OuBALhLhF91KayzGhRSzXHqA75iUw==
 
-flow-remove-types@^2.272:
+flow-remove-types@^2.273:
   version "2.279.0"
   resolved "https://registry.yarnpkg.com/flow-remove-types/-/flow-remove-types-2.279.0.tgz#3a3388d9158eba0f82c40d80d31d9640b883a3f5"
   integrity sha512-bPFloMR/A2b/r/sIsf7Ix0LaMicCJNjwhXc4xEEQVzJCIz5u7C7XDaEOXOiqveKlCYK7DcBNn6R01Cbbc9gsYA==