straightford explicit types

packages/react-debug-tools/src/ReactDebugHooks.js

@@ -783,7 +783,7 @@ export function inspectHooksOfFiber(
   fiber: Fiber,
   currentDispatcher: ?CurrentDispatcherRef,
   includeHooksSource?: boolean = false,
-) {
+): HooksTree {
   // DevTools will pass the current renderer's injected dispatcher.
   // Other apps might compile debug hooks as part of their app though.
   if (currentDispatcher == null) {

packages/react-dom/src/client/ReactDOMHostConfig.js

@@ -677,7 +677,7 @@ export function clearContainer(container: Container): void {
 
 export const supportsHydration = true;
 
-export function isHydratableResource(type: string, props: Props) {
+export function isHydratableResource(type: string, props: Props): boolean {
   return (
     type === 'link' &&
     typeof (props: any).precedence === 'string' &&
@@ -723,11 +723,13 @@ export function canHydrateSuspenseInstance(
   return ((instance: any): SuspenseInstance);
 }
 
-export function isSuspenseInstancePending(instance: SuspenseInstance) {
+export function isSuspenseInstancePending(instance: SuspenseInstance): boolean {
   return instance.data === SUSPENSE_PENDING_START_DATA;
 }
 
-export function isSuspenseInstanceFallback(instance: SuspenseInstance) {
+export function isSuspenseInstanceFallback(
+  instance: SuspenseInstance,
+): boolean {
   return instance.data === SUSPENSE_FALLBACK_START_DATA;
 }
 

packages/react-dom/src/client/inputValueTracking.js

@@ -123,7 +123,7 @@ export function track(node: ElementWithValueTracker) {
   node._valueTracker = trackValueOnNode(node);
 }
 
-export function updateValueIfChanged(node: ElementWithValueTracker) {
+export function updateValueIfChanged(node: ElementWithValueTracker): boolean {
   if (!node) {
     return false;
   }

packages/react-dom/src/events/checkPassiveEvents.js

@@ -9,7 +9,7 @@
 
 import {canUseDOM} from 'shared/ExecutionEnvironment';
 
-export let passiveBrowserEventsSupported = false;
+export let passiveBrowserEventsSupported: boolean = false;
 
 // Check if browser support events with passive listeners
 // https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#Safely_detecting_option_support

packages/react-dom/src/shared/DOMProperty.js

@@ -63,10 +63,10 @@ export type PropertyInfo = {
 export const ATTRIBUTE_NAME_START_CHAR =
   ':A-Z_a-z\\u00C0-\\u00D6\\u00D8-\\u00F6\\u00F8-\\u02FF\\u0370-\\u037D\\u037F-\\u1FFF\\u200C-\\u200D\\u2070-\\u218F\\u2C00-\\u2FEF\\u3001-\\uD7FF\\uF900-\\uFDCF\\uFDF0-\\uFFFD';
 /* eslint-enable max-len */
-export const ATTRIBUTE_NAME_CHAR =
+export const ATTRIBUTE_NAME_CHAR: string =
   ATTRIBUTE_NAME_START_CHAR + '\\-.0-9\\u00B7\\u0300-\\u036F\\u203F-\\u2040';
 
-export const VALID_ATTRIBUTE_NAME_REGEX = new RegExp(
+export const VALID_ATTRIBUTE_NAME_REGEX: RegExp = new RegExp(
   '^[' + ATTRIBUTE_NAME_START_CHAR + '][' + ATTRIBUTE_NAME_CHAR + ']*$',
 );
 

packages/react-dom/src/shared/isCustomComponent.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-function isCustomComponent(tagName: string, props: Object) {
+function isCustomComponent(tagName: string, props: Object): boolean {
   if (tagName.indexOf('-') === -1) {
     return typeof props.is === 'string';
   }

packages/react-is/src/ReactIs.js

@@ -82,7 +82,7 @@ let hasWarnedAboutDeprecatedIsAsyncMode = false;
 let hasWarnedAboutDeprecatedIsConcurrentMode = false;
 
 // AsyncMode should be deprecated
-export function isAsyncMode(object: any) {
+export function isAsyncMode(object: any): boolean {
   if (__DEV__) {
     if (!hasWarnedAboutDeprecatedIsAsyncMode) {
       hasWarnedAboutDeprecatedIsAsyncMode = true;
@@ -95,7 +95,7 @@ export function isAsyncMode(object: any) {
   }
   return false;
 }
-export function isConcurrentMode(object: any) {
+export function isConcurrentMode(object: any): boolean {
   if (__DEV__) {
     if (!hasWarnedAboutDeprecatedIsConcurrentMode) {
       hasWarnedAboutDeprecatedIsConcurrentMode = true;
@@ -108,43 +108,43 @@ export function isConcurrentMode(object: any) {
   }
   return false;
 }
-export function isContextConsumer(object: any) {
+export function isContextConsumer(object: any): boolean {
   return typeOf(object) === REACT_CONTEXT_TYPE;
 }
-export function isContextProvider(object: any) {
+export function isContextProvider(object: any): boolean {
   return typeOf(object) === REACT_PROVIDER_TYPE;
 }
-export function isElement(object: any) {
+export function isElement(object: any): boolean {
   return (
     typeof object === 'object' &&
     object !== null &&
     object.$$typeof === REACT_ELEMENT_TYPE
   );
 }
-export function isForwardRef(object: any) {
+export function isForwardRef(object: any): boolean {
   return typeOf(object) === REACT_FORWARD_REF_TYPE;
 }
-export function isFragment(object: any) {
+export function isFragment(object: any): boolean {
   return typeOf(object) === REACT_FRAGMENT_TYPE;
 }
-export function isLazy(object: any) {
+export function isLazy(object: any): boolean {
   return typeOf(object) === REACT_LAZY_TYPE;
 }
-export function isMemo(object: any) {
+export function isMemo(object: any): boolean {
   return typeOf(object) === REACT_MEMO_TYPE;
 }
-export function isPortal(object: any) {
+export function isPortal(object: any): boolean {
   return typeOf(object) === REACT_PORTAL_TYPE;
 }
-export function isProfiler(object: any) {
+export function isProfiler(object: any): boolean {
   return typeOf(object) === REACT_PROFILER_TYPE;
 }
-export function isStrictMode(object: any) {
+export function isStrictMode(object: any): boolean {
   return typeOf(object) === REACT_STRICT_MODE_TYPE;
 }
-export function isSuspense(object: any) {
+export function isSuspense(object: any): boolean {
   return typeOf(object) === REACT_SUSPENSE_TYPE;
 }
-export function isSuspenseList(object: any) {
+export function isSuspenseList(object: any): boolean {
   return typeOf(object) === REACT_SUSPENSE_LIST_TYPE;
 }

packages/react-reconciler/src/ReactCurrentFiber.js

@@ -73,7 +73,7 @@ export function setIsRendering(rendering: boolean) {
   }
 }
 
-export function getIsRendering() {
+export function getIsRendering(): void | boolean {
   if (__DEV__) {
     return isRendering;
   }

packages/react-reconciler/src/ReactEventPriorities.js

@@ -58,7 +58,7 @@ export function getCurrentUpdatePriority(): EventPriority {
     : (getCurrentUpdatePriority_old(): any);
 }
 
-export function setCurrentUpdatePriority(priority: EventPriority) {
+export function setCurrentUpdatePriority(priority: EventPriority): void {
   return enableNewReconciler
     ? setCurrentUpdatePriority_new((priority: any))
     : setCurrentUpdatePriority_old((priority: any));

packages/react-reconciler/src/ReactFiber.new.js

@@ -225,7 +225,7 @@ function shouldConstruct(Component: Function) {
   return !!(prototype && prototype.isReactComponent);
 }
 
-export function isSimpleFunctionComponent(type: any) {
+export function isSimpleFunctionComponent(type: any): boolean {
   return (
     typeof type === 'function' &&
     !shouldConstruct(type) &&
@@ -355,7 +355,10 @@ export function createWorkInProgress(current: Fiber, pendingProps: any): Fiber {
 }
 
 // Used to reuse a Fiber for a second pass.
-export function resetWorkInProgress(workInProgress: Fiber, renderLanes: Lanes) {
+export function resetWorkInProgress(
+  workInProgress: Fiber,
+  renderLanes: Lanes,
+): Fiber {
   // This resets the Fiber to what createFiber or createWorkInProgress would
   // have set the values to before during the first pass. Ideally this wouldn't
   // be necessary but unfortunately many code paths reads from the workInProgress

packages/react-reconciler/src/ReactFiberAct.new.js

@@ -15,7 +15,7 @@ import {warnsIfNotActing} from './ReactFiberHostConfig';
 
 const {ReactCurrentActQueue} = ReactSharedInternals;
 
-export function isLegacyActEnvironment(fiber: Fiber) {
+export function isLegacyActEnvironment(fiber: Fiber): boolean {
   if (__DEV__) {
     // Legacy mode. We preserve the behavior of React 17's act. It assumes an
     // act environment whenever `jest` is defined, but you can still turn off

packages/react-reconciler/src/ReactFiberBeginWork.new.js

@@ -281,7 +281,7 @@ let didWarnAboutModulePatternComponent;
 let didWarnAboutContextTypeOnFunctionComponent;
 let didWarnAboutGetDerivedStateOnFunctionComponent;
 let didWarnAboutFunctionRefs;
-export let didWarnAboutReassigningProps;
+export let didWarnAboutReassigningProps: boolean;
 let didWarnAboutRevealOrder;
 let didWarnAboutTailOptions;
 let didWarnAboutDefaultPropsOnFunctionComponent;
@@ -3479,7 +3479,7 @@ export function markWorkInProgressReceivedUpdate() {
   didReceiveUpdate = true;
 }
 
-export function checkIfWorkInProgressReceivedUpdate() {
+export function checkIfWorkInProgressReceivedUpdate(): boolean {
   return didReceiveUpdate;
 }
 

packages/react-reconciler/src/ReactFiberClassUpdateQueue.new.js

@@ -164,7 +164,7 @@ let hasForceUpdate = false;
 
 let didWarnUpdateInsideUpdate;
 let currentlyProcessingQueue;
-export let resetCurrentlyProcessingQueue;
+export let resetCurrentlyProcessingQueue: () => void;
 if (__DEV__) {
   didWarnUpdateInsideUpdate = false;
   currentlyProcessingQueue = null;

packages/react-reconciler/src/ReactFiberCommitWork.new.js

@@ -320,7 +320,7 @@ let shouldFireAfterActiveInstanceBlur: boolean = false;
 export function commitBeforeMutationEffects(
   root: FiberRoot,
   firstChild: Fiber,
-) {
+): boolean {
   focusedInstanceHandle = prepareForCommit(root.containerInfo);
 
   nextEffect = firstChild;

packages/react-reconciler/src/ReactFiberHiddenContext.new.js

@@ -66,6 +66,6 @@ export function popHiddenContext(fiber: Fiber): void {
   pop(prevRenderLanesStackCursor, fiber);
 }
 
-export function isCurrentTreeHidden() {
+export function isCurrentTreeHidden(): boolean {
   return currentTreeHiddenStackCursor.current !== null;
 }

packages/react-reconciler/src/ReactFiberHooks.new.js

@@ -564,7 +564,7 @@ export function renderWithHooks<Props, SecondArg>(
   return children;
 }
 
-export function checkDidRenderIdHook() {
+export function checkDidRenderIdHook(): boolean {
   // This should be called immediately after every renderWithHooks call.
   // Conceptually, it's part of the return value of renderWithHooks; it's only a
   // separate function to avoid using an array tuple.

packages/react-reconciler/src/ReactFiberHotReloading.js

@@ -7,6 +7,8 @@
  * @flow
  */
 
+import type {Fiber} from './ReactInternalTypes';
+import type {ReactElement} from '../../shared/ReactElementType';
 import type {Instance} from './ReactFiberHostConfig';
 import type {FiberRoot} from './ReactInternalTypes';
 import type {ReactNodeList} from 'shared/ReactTypes';
@@ -58,9 +60,9 @@ export type FindHostInstancesForRefresh = (
   families: Array<Family>,
 ) => Set<Instance>;
 
-export const setRefreshHandler = enableNewReconciler
-  ? setRefreshHandler_new
-  : setRefreshHandler_old;
+export const setRefreshHandler: (
+  handler: RefreshHandler | null,
+) => void = enableNewReconciler ? setRefreshHandler_new : setRefreshHandler_old;
 export const resolveFunctionForHotReloading = enableNewReconciler
   ? resolveFunctionForHotReloading_new
   : resolveFunctionForHotReloading_old;
@@ -70,18 +72,23 @@ export const resolveClassForHotReloading = enableNewReconciler
 export const resolveForwardRefForHotReloading = enableNewReconciler
   ? resolveForwardRefForHotReloading_new
   : resolveForwardRefForHotReloading_old;
-export const isCompatibleFamilyForHotReloading = enableNewReconciler
+export const isCompatibleFamilyForHotReloading: (
+  fiber: Fiber,
+  element: ReactElement,
+) => boolean = enableNewReconciler
   ? isCompatibleFamilyForHotReloading_new
   : isCompatibleFamilyForHotReloading_old;
-export const markFailedErrorBoundaryForHotReloading = enableNewReconciler
+export const markFailedErrorBoundaryForHotReloading: (
+  fiber: Fiber,
+) => void = enableNewReconciler
   ? markFailedErrorBoundaryForHotReloading_new
   : markFailedErrorBoundaryForHotReloading_old;
-export const scheduleRefresh = enableNewReconciler
+export const scheduleRefresh: ScheduleRefresh = enableNewReconciler
   ? scheduleRefresh_new
   : scheduleRefresh_old;
-export const scheduleRoot = enableNewReconciler
+export const scheduleRoot: ScheduleRoot = enableNewReconciler
   ? scheduleRoot_new
   : scheduleRoot_old;
-export const findHostInstancesForRefresh = enableNewReconciler
+export const findHostInstancesForRefresh: FindHostInstancesForRefresh = enableNewReconciler
   ? findHostInstancesForRefresh_new
   : findHostInstancesForRefresh_old;

packages/react-reconciler/src/ReactFiberHydrationContext.new.js

@@ -109,7 +109,7 @@ export function markDidThrowWhileHydratingDEV() {
   }
 }
 
-export function didSuspendOrErrorWhileHydratingDEV() {
+export function didSuspendOrErrorWhileHydratingDEV(): boolean {
   if (__DEV__) {
     return didSuspendOrErrorDEV;
   }
@@ -685,7 +685,7 @@ function popHydrationState(fiber: Fiber): boolean {
   return true;
 }
 
-function hasUnhydratedTailNodes() {
+function hasUnhydratedTailNodes(): boolean {
   return isHydrating && nextHydratableInstance !== null;
 }
 

packages/react-reconciler/src/ReactFiberLane.new.js

@@ -435,7 +435,7 @@ export function markStarvedLanesAsExpired(
 
 // This returns the highest priority pending lanes regardless of whether they
 // are suspended.
-export function getHighestPriorityPendingLanes(root: FiberRoot) {
+export function getHighestPriorityPendingLanes(root: FiberRoot): Lanes {
   return getHighestPriorityLanes(root.pendingLanes);
 }
 
@@ -458,25 +458,25 @@ export function getLanesToRetrySynchronouslyOnError(
   return NoLanes;
 }
 
-export function includesSyncLane(lanes: Lanes) {
+export function includesSyncLane(lanes: Lanes): boolean {
   return (lanes & SyncLane) !== NoLanes;
 }
 
-export function includesNonIdleWork(lanes: Lanes) {
+export function includesNonIdleWork(lanes: Lanes): boolean {
   return (lanes & NonIdleLanes) !== NoLanes;
 }
-export function includesOnlyRetries(lanes: Lanes) {
+export function includesOnlyRetries(lanes: Lanes): boolean {
   return (lanes & RetryLanes) === lanes;
 }
-export function includesOnlyNonUrgentLanes(lanes: Lanes) {
+export function includesOnlyNonUrgentLanes(lanes: Lanes): boolean {
   const UrgentLanes = SyncLane | InputContinuousLane | DefaultLane;
   return (lanes & UrgentLanes) === NoLanes;
 }
-export function includesOnlyTransitions(lanes: Lanes) {
+export function includesOnlyTransitions(lanes: Lanes): boolean {
   return (lanes & TransitionLanes) === lanes;
 }
 
-export function includesBlockingLane(root: FiberRoot, lanes: Lanes) {
+export function includesBlockingLane(root: FiberRoot, lanes: Lanes): boolean {
   if (
     allowConcurrentByDefault &&
     (root.current.mode & ConcurrentUpdatesByDefaultMode) !== NoMode
@@ -492,13 +492,13 @@ export function includesBlockingLane(root: FiberRoot, lanes: Lanes) {
   return (lanes & SyncDefaultLanes) !== NoLanes;
 }
 
-export function includesExpiredLane(root: FiberRoot, lanes: Lanes) {
+export function includesExpiredLane(root: FiberRoot, lanes: Lanes): boolean {
   // This is a separate check from includesBlockingLane because a lane can
   // expire after a render has already started.
   return (lanes & root.expiredLanes) !== NoLanes;
 }
 
-export function isTransitionLane(lane: Lane) {
+export function isTransitionLane(lane: Lane): boolean {
   return (lane & TransitionLanes) !== NoLanes;
 }
 
@@ -543,11 +543,11 @@ function laneToIndex(lane: Lane) {
   return pickArbitraryLaneIndex(lane);
 }
 
-export function includesSomeLane(a: Lanes | Lane, b: Lanes | Lane) {
+export function includesSomeLane(a: Lanes | Lane, b: Lanes | Lane): boolean {
   return (a & b) !== NoLanes;
 }
 
-export function isSubsetOfLanes(set: Lanes, subset: Lanes | Lane) {
+export function isSubsetOfLanes(set: Lanes, subset: Lanes | Lane): boolean {
   return (set & subset) === subset;
 }
 
@@ -569,7 +569,7 @@ export function laneToLanes(lane: Lane): Lanes {
   return lane;
 }
 
-export function higherPriorityLane(a: Lane, b: Lane) {
+export function higherPriorityLane(a: Lane, b: Lane): Lane {
   // This works because the bit ranges decrease in priority as you go left.
   return a !== NoLane && a < b ? a : b;
 }