From b4f119cdf1defe2437e00022f670c6ef818cd43f Mon Sep 17 00:00:00 2001
From: Sebastian Markbage <sema@fb.com>
Date: Thu, 1 Apr 2021 15:19:00 -0400
Subject: [PATCH] Revert "Remove redundant initial of isArray (#21163)"

This reverts commit b130a0f5cd4f29a1c3147f66e10914c42847678a.
---
 .../eslint-plugin-react-hooks/src/ExhaustiveDeps.js | 10 ++++------
 packages/jest-react/src/JestReact.js                |  3 +--
 .../react-devtools-shared/src/backend/renderer.js   |  3 +--
 packages/react-devtools-shared/src/backend/utils.js | 11 +++++------
 packages/react-dom/src/client/ReactDOMSelect.js     |  7 +++----
 packages/react-dom/src/client/ReactDOMTextarea.js   |  4 ++--
 .../src/server/ReactDOMServerFormatConfig.js        |  3 ++-
 .../react-dom/src/server/ReactPartialRenderer.js    | 11 +++++------
 packages/react-dom/src/test-utils/ReactTestUtils.js |  7 +++----
 .../src/ReactNativeAttributePayload.js              | 13 ++++++-------
 .../src/legacy-events/EventPluginUtils.js           | 11 +++++------
 .../src/legacy-events/accumulate.js                 |  5 ++---
 .../src/legacy-events/accumulateInto.js             |  7 +++----
 packages/react-noop-renderer/src/createReactNoop.js |  9 ++++-----
 .../react-reconciler/src/ReactChildFiber.new.js     |  3 ++-
 .../react-reconciler/src/ReactChildFiber.old.js     |  3 ++-
 .../src/ReactFiberClassComponent.new.js             |  2 +-
 .../src/ReactFiberClassComponent.old.js             |  2 +-
 .../src/ReactFiberReconciler.new.js                 | 11 +++++------
 .../src/ReactFiberReconciler.old.js                 | 11 +++++------
 .../src/ReactFlightDOMRelayServerHostConfig.js      |  3 +--
 .../src/ReactFlightNativeRelayServerHostConfig.js   |  4 ++--
 packages/react-server/src/ReactFizzServer.js        |  3 +--
 packages/react-server/src/ReactFlightServer.js      |  3 ++-
 packages/react/src/ReactChildren.js                 |  5 ++---
 packages/react/src/ReactElementValidator.js         |  9 ++++-----
 packages/react/src/jsx/ReactJSXElementValidator.js  |  7 +++----
 packages/shared/isArray.js                          | 12 ------------
 28 files changed, 77 insertions(+), 105 deletions(-)
 delete mode 100644 packages/shared/isArray.js

diff --git a/packages/eslint-plugin-react-hooks/src/ExhaustiveDeps.js b/packages/eslint-plugin-react-hooks/src/ExhaustiveDeps.js
index 268b6873bd589..2c76ca5991f76 100644
--- a/packages/eslint-plugin-react-hooks/src/ExhaustiveDeps.js
+++ b/packages/eslint-plugin-react-hooks/src/ExhaustiveDeps.js
@@ -145,8 +145,6 @@ export default {
         componentScope = currentScope;
       }
 
-      const isArray = Array.isArray;
-
       // Next we'll define a few helpers that helps us
       // tell if some values don't have to be declared as deps.
 
@@ -159,7 +157,7 @@ export default {
       //       ^^^ true for this reference
       // False for everything else.
       function isStableKnownHookValue(resolved) {
-        if (!isArray(resolved.defs)) {
+        if (!Array.isArray(resolved.defs)) {
           return false;
         }
         const def = resolved.defs[0];
@@ -228,7 +226,7 @@ export default {
           if (
             id.type === 'ArrayPattern' &&
             id.elements.length === 2 &&
-            isArray(resolved.identifiers)
+            Array.isArray(resolved.identifiers)
           ) {
             // Is second tuple value the same reference we're checking?
             if (id.elements[1] === resolved.identifiers[0]) {
@@ -257,7 +255,7 @@ export default {
         } else if (name === 'useTransition') {
           if (
             id.type === 'ArrayPattern' &&
-            isArray(resolved.identifiers)
+            Array.isArray(resolved.identifiers)
           ) {
             // Is first tuple value the same reference we're checking?
             if (id.elements[0] === resolved.identifiers[0]) {
@@ -272,7 +270,7 @@ export default {
 
       // Some are just functions that don't reference anything dynamic.
       function isFunctionWithoutCapturedValues(resolved) {
-        if (!isArray(resolved.defs)) {
+        if (!Array.isArray(resolved.defs)) {
           return false;
         }
         const def = resolved.defs[0];
diff --git a/packages/jest-react/src/JestReact.js b/packages/jest-react/src/JestReact.js
index 1f26cbee3a328..57790797b966d 100644
--- a/packages/jest-react/src/JestReact.js
+++ b/packages/jest-react/src/JestReact.js
@@ -8,7 +8,6 @@
 import {REACT_ELEMENT_TYPE, REACT_FRAGMENT_TYPE} from 'shared/ReactSymbols';
 
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 
 function captureAssertion(fn) {
   // Trick to use a Jest matcher inside another Jest matcher. `fn` contains an
@@ -43,7 +42,7 @@ export function unstable_toMatchRenderedOutput(root, expectedJSX) {
   let actualJSX;
   if (actualJSON === null || typeof actualJSON === 'string') {
     actualJSX = actualJSON;
-  } else if (isArray(actualJSON)) {
+  } else if (Array.isArray(actualJSON)) {
     if (actualJSON.length === 0) {
       actualJSX = null;
     } else if (actualJSON.length === 1) {
diff --git a/packages/react-devtools-shared/src/backend/renderer.js b/packages/react-devtools-shared/src/backend/renderer.js
index c61edb45daa65..050a4e709ab32 100644
--- a/packages/react-devtools-shared/src/backend/renderer.js
+++ b/packages/react-devtools-shared/src/backend/renderer.js
@@ -105,7 +105,6 @@ import type {
   ElementType,
 } from 'react-devtools-shared/src/types';
 import is from 'shared/objectIs';
-import isArray from 'shared/isArray';
 
 type getDisplayNameForFiberType = (fiber: Fiber) => string | null;
 type getTypeSymbolType = (type: any) => Symbol | number;
@@ -1138,7 +1137,7 @@ export function attach(
       memoizedState.hasOwnProperty('create') &&
       memoizedState.hasOwnProperty('destroy') &&
       memoizedState.hasOwnProperty('deps') &&
-      (memoizedState.deps === null || isArray(memoizedState.deps)) &&
+      (memoizedState.deps === null || Array.isArray(memoizedState.deps)) &&
       memoizedState.hasOwnProperty('next')
     );
   }
diff --git a/packages/react-devtools-shared/src/backend/utils.js b/packages/react-devtools-shared/src/backend/utils.js
index 593459d78f646..7a4ff6295ab99 100644
--- a/packages/react-devtools-shared/src/backend/utils.js
+++ b/packages/react-devtools-shared/src/backend/utils.js
@@ -9,7 +9,6 @@
 
 import {copy} from 'clipboard-js';
 import {dehydrate} from '../hydration';
-import isArray from 'shared/isArray';
 
 import type {DehydratedData} from 'react-devtools-shared/src/devtools/views/Components/types';
 
@@ -62,9 +61,9 @@ export function copyWithDelete(
   index: number = 0,
 ): Object | Array<any> {
   const key = path[index];
-  const updated = isArray(obj) ? obj.slice() : {...obj};
+  const updated = Array.isArray(obj) ? obj.slice() : {...obj};
   if (index + 1 === path.length) {
-    if (isArray(updated)) {
+    if (Array.isArray(updated)) {
       updated.splice(((key: any): number), 1);
     } else {
       delete updated[key];
@@ -85,12 +84,12 @@ export function copyWithRename(
   index: number = 0,
 ): Object | Array<any> {
   const oldKey = oldPath[index];
-  const updated = isArray(obj) ? obj.slice() : {...obj};
+  const updated = Array.isArray(obj) ? obj.slice() : {...obj};
   if (index + 1 === oldPath.length) {
     const newKey = newPath[index];
     // $FlowFixMe number or string is fine here
     updated[newKey] = updated[oldKey];
-    if (isArray(updated)) {
+    if (Array.isArray(updated)) {
       updated.splice(((oldKey: any): number), 1);
     } else {
       delete updated[oldKey];
@@ -112,7 +111,7 @@ export function copyWithSet(
     return value;
   }
   const key = path[index];
-  const updated = isArray(obj) ? obj.slice() : {...obj};
+  const updated = Array.isArray(obj) ? obj.slice() : {...obj};
   // $FlowFixMe number or string is fine here
   updated[key] = copyWithSet(obj[key], path, value, index + 1);
   return updated;
diff --git a/packages/react-dom/src/client/ReactDOMSelect.js b/packages/react-dom/src/client/ReactDOMSelect.js
index df336d4b92254..1efca61905b4a 100644
--- a/packages/react-dom/src/client/ReactDOMSelect.js
+++ b/packages/react-dom/src/client/ReactDOMSelect.js
@@ -12,7 +12,6 @@ import {getCurrentFiberOwnerNameInDevOrNull} from 'react-reconciler/src/ReactCur
 
 import {checkControlledValueProps} from '../shared/ReactControlledValuePropTypes';
 import {getToStringValue, toString} from './ToStringValue';
-import isArray from 'shared/isArray';
 
 let didWarnValueDefaultValue;
 
@@ -46,15 +45,15 @@ function checkSelectPropTypes(props) {
       if (props[propName] == null) {
         continue;
       }
-      const propNameIsArray = isArray(props[propName]);
-      if (props.multiple && !propNameIsArray) {
+      const isArray = Array.isArray(props[propName]);
+      if (props.multiple && !isArray) {
         console.error(
           'The `%s` prop supplied to <select> must be an array if ' +
             '`multiple` is true.%s',
           propName,
           getDeclarationErrorAddendum(),
         );
-      } else if (!props.multiple && propNameIsArray) {
+      } else if (!props.multiple && isArray) {
         console.error(
           'The `%s` prop supplied to <select> must be a scalar ' +
             'value if `multiple` is false.%s',
diff --git a/packages/react-dom/src/client/ReactDOMTextarea.js b/packages/react-dom/src/client/ReactDOMTextarea.js
index 6e8aed5cc43cd..24fb591fcd8af 100644
--- a/packages/react-dom/src/client/ReactDOMTextarea.js
+++ b/packages/react-dom/src/client/ReactDOMTextarea.js
@@ -8,12 +8,12 @@
  */
 
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 
 import {checkControlledValueProps} from '../shared/ReactControlledValuePropTypes';
 import {getCurrentFiberOwnerNameInDevOrNull} from 'react-reconciler/src/ReactCurrentFiber';
 import {getToStringValue, toString} from './ToStringValue';
 import type {ToStringValue} from './ToStringValue';
+
 import {disableTextareaChildren} from 'shared/ReactFeatureFlags';
 
 let didWarnValDefaultVal = false;
@@ -100,7 +100,7 @@ export function initWrapperState(element: Element, props: Object) {
           defaultValue == null,
           'If you supply `defaultValue` on a <textarea>, do not pass children.',
         );
-        if (isArray(children)) {
+        if (Array.isArray(children)) {
           invariant(
             children.length <= 1,
             '<textarea> can only have at most one child.',
diff --git a/packages/react-dom/src/server/ReactDOMServerFormatConfig.js b/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
index 45cd0fecb5e96..2988e9a588334 100644
--- a/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
+++ b/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
@@ -46,7 +46,8 @@ import hyphenateStyleName from '../shared/hyphenateStyleName';
 import invariant from 'shared/invariant';
 import hasOwnProperty from 'shared/hasOwnProperty';
 import sanitizeURL from '../shared/sanitizeURL';
-import isArray from 'shared/isArray';
+
+const isArray = Array.isArray;
 
 // Per response, global state that is not contextual to the rendering subtree.
 export type ResponseState = {
diff --git a/packages/react-dom/src/server/ReactPartialRenderer.js b/packages/react-dom/src/server/ReactPartialRenderer.js
index 90fbfd6ad4391..4d2aeb5b38f81 100644
--- a/packages/react-dom/src/server/ReactPartialRenderer.js
+++ b/packages/react-dom/src/server/ReactPartialRenderer.js
@@ -14,7 +14,6 @@ import type {ReactProvider, ReactContext} from 'shared/ReactTypes';
 
 import * as React from 'react';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import {describeUnknownElementTypeFrameInDEV} from 'shared/ReactComponentStackFrame';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
@@ -1439,7 +1438,7 @@ class ReactDOMServerRenderer {
             defaultValue == null,
             'If you supply `defaultValue` on a <textarea>, do not pass children.',
           );
-          if (isArray(textareaChildren)) {
+          if (Array.isArray(textareaChildren)) {
             invariant(
               textareaChildren.length <= 1,
               '<textarea> can only have at most one child.',
@@ -1468,14 +1467,14 @@ class ReactDOMServerRenderer {
           if (props[propName] == null) {
             continue;
           }
-          const propNameIsArray = isArray(props[propName]);
-          if (props.multiple && !propNameIsArray) {
+          const isArray = Array.isArray(props[propName]);
+          if (props.multiple && !isArray) {
             console.error(
               'The `%s` prop supplied to <select> must be an array if ' +
                 '`multiple` is true.',
               propName,
             );
-          } else if (!props.multiple && propNameIsArray) {
+          } else if (!props.multiple && isArray) {
             console.error(
               'The `%s` prop supplied to <select> must be a scalar ' +
                 'value if `multiple` is false.',
@@ -1516,7 +1515,7 @@ class ReactDOMServerRenderer {
           value = optionChildren;
         }
         selected = false;
-        if (isArray(selectValue)) {
+        if (Array.isArray(selectValue)) {
           // multiple
           for (let j = 0; j < selectValue.length; j++) {
             if ('' + selectValue[j] === value) {
diff --git a/packages/react-dom/src/test-utils/ReactTestUtils.js b/packages/react-dom/src/test-utils/ReactTestUtils.js
index 492ab02d11929..dc59d2a64420f 100644
--- a/packages/react-dom/src/test-utils/ReactTestUtils.js
+++ b/packages/react-dom/src/test-utils/ReactTestUtils.js
@@ -24,7 +24,6 @@ import {
   rethrowCaughtError,
   invokeGuardedCallbackAndCatchFirstError,
 } from 'shared/ReactErrorUtils';
-import isArray from 'shared/isArray';
 
 // Keep in sync with ReactDOM.js, and ReactTestUtilsAct.js:
 const EventInternals =
@@ -98,7 +97,7 @@ function validateClassInstance(inst, methodName) {
   }
   let received;
   const stringified = '' + inst;
-  if (isArray(inst)) {
+  if (Array.isArray(inst)) {
     received = 'an array';
   } else if (inst && inst.nodeType === ELEMENT_NODE && inst.tagName) {
     received = 'a DOM node';
@@ -198,7 +197,7 @@ function scryRenderedDOMComponentsWithClass(root, classNames) {
       }
       const classList = className.split(/\s+/);
 
-      if (!isArray(classNames)) {
+      if (!Array.isArray(classNames)) {
         invariant(
           classNames !== undefined,
           'TestUtils.scryRenderedDOMComponentsWithClass expects a ' +
@@ -366,7 +365,7 @@ function executeDispatch(event, listener, inst) {
 function executeDispatchesInOrder(event) {
   const dispatchListeners = event._dispatchListeners;
   const dispatchInstances = event._dispatchInstances;
-  if (isArray(dispatchListeners)) {
+  if (Array.isArray(dispatchListeners)) {
     for (let i = 0; i < dispatchListeners.length; i++) {
       if (event.isPropagationStopped()) {
         break;
diff --git a/packages/react-native-renderer/src/ReactNativeAttributePayload.js b/packages/react-native-renderer/src/ReactNativeAttributePayload.js
index d388f4046a011..fa1187bc339bc 100644
--- a/packages/react-native-renderer/src/ReactNativeAttributePayload.js
+++ b/packages/react-native-renderer/src/ReactNativeAttributePayload.js
@@ -12,7 +12,6 @@ import {
   deepDiffer,
   flattenStyle,
 } from 'react-native/Libraries/ReactPrivate/ReactNativePrivateInterface';
-import isArray from 'shared/isArray';
 
 import type {AttributeConfiguration} from './ReactNativeTypes';
 
@@ -52,7 +51,7 @@ function restoreDeletedValuesInNestedArray(
   node: NestedNode,
   validAttributes: AttributeConfiguration,
 ) {
-  if (isArray(node)) {
+  if (Array.isArray(node)) {
     let i = node.length;
     while (i-- && removedKeyCount > 0) {
       restoreDeletedValuesInNestedArray(
@@ -164,12 +163,12 @@ function diffNestedProperty(
     return updatePayload;
   }
 
-  if (!isArray(prevProp) && !isArray(nextProp)) {
+  if (!Array.isArray(prevProp) && !Array.isArray(nextProp)) {
     // Both are leaves, we can diff the leaves.
     return diffProperties(updatePayload, prevProp, nextProp, validAttributes);
   }
 
-  if (isArray(prevProp) && isArray(nextProp)) {
+  if (Array.isArray(prevProp) && Array.isArray(nextProp)) {
     // Both are arrays, we can diff the arrays.
     return diffNestedArrayProperty(
       updatePayload,
@@ -179,7 +178,7 @@ function diffNestedProperty(
     );
   }
 
-  if (isArray(prevProp)) {
+  if (Array.isArray(prevProp)) {
     return diffProperties(
       updatePayload,
       // $FlowFixMe - We know that this is always an object when the input is.
@@ -213,7 +212,7 @@ function addNestedProperty(
     return updatePayload;
   }
 
-  if (!isArray(nextProp)) {
+  if (!Array.isArray(nextProp)) {
     // Add each property of the leaf.
     return addProperties(updatePayload, nextProp, validAttributes);
   }
@@ -243,7 +242,7 @@ function clearNestedProperty(
     return updatePayload;
   }
 
-  if (!isArray(prevProp)) {
+  if (!Array.isArray(prevProp)) {
     // Add each property of the leaf.
     return clearProperties(updatePayload, prevProp, validAttributes);
   }
diff --git a/packages/react-native-renderer/src/legacy-events/EventPluginUtils.js b/packages/react-native-renderer/src/legacy-events/EventPluginUtils.js
index 381ebafc59bb3..abba8e9a3dabe 100644
--- a/packages/react-native-renderer/src/legacy-events/EventPluginUtils.js
+++ b/packages/react-native-renderer/src/legacy-events/EventPluginUtils.js
@@ -7,7 +7,6 @@
 
 import {invokeGuardedCallbackAndCatchFirstError} from 'shared/ReactErrorUtils';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 
 export let getFiberCurrentPropsFromNode = null;
 export let getInstanceFromNode = null;
@@ -37,14 +36,14 @@ if (__DEV__) {
     const dispatchListeners = event._dispatchListeners;
     const dispatchInstances = event._dispatchInstances;
 
-    const listenersIsArr = isArray(dispatchListeners);
+    const listenersIsArr = Array.isArray(dispatchListeners);
     const listenersLen = listenersIsArr
       ? dispatchListeners.length
       : dispatchListeners
       ? 1
       : 0;
 
-    const instancesIsArr = isArray(dispatchInstances);
+    const instancesIsArr = Array.isArray(dispatchInstances);
     const instancesLen = instancesIsArr
       ? dispatchInstances.length
       : dispatchInstances
@@ -79,7 +78,7 @@ export function executeDispatchesInOrder(event) {
   if (__DEV__) {
     validateEventDispatches(event);
   }
-  if (isArray(dispatchListeners)) {
+  if (Array.isArray(dispatchListeners)) {
     for (let i = 0; i < dispatchListeners.length; i++) {
       if (event.isPropagationStopped()) {
         break;
@@ -107,7 +106,7 @@ function executeDispatchesInOrderStopAtTrueImpl(event) {
   if (__DEV__) {
     validateEventDispatches(event);
   }
-  if (isArray(dispatchListeners)) {
+  if (Array.isArray(dispatchListeners)) {
     for (let i = 0; i < dispatchListeners.length; i++) {
       if (event.isPropagationStopped()) {
         break;
@@ -151,7 +150,7 @@ export function executeDirectDispatch(event) {
   const dispatchListener = event._dispatchListeners;
   const dispatchInstance = event._dispatchInstances;
   invariant(
-    !isArray(dispatchListener),
+    !Array.isArray(dispatchListener),
     'executeDirectDispatch(...): Invalid `event`.',
   );
   event.currentTarget = dispatchListener
diff --git a/packages/react-native-renderer/src/legacy-events/accumulate.js b/packages/react-native-renderer/src/legacy-events/accumulate.js
index af4da853934b0..6fcf9f1fd80c0 100644
--- a/packages/react-native-renderer/src/legacy-events/accumulate.js
+++ b/packages/react-native-renderer/src/legacy-events/accumulate.js
@@ -8,7 +8,6 @@
  */
 
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 
 /**
  * Accumulates items that must not be null or undefined.
@@ -32,11 +31,11 @@ function accumulate<T>(
 
   // Both are not empty. Warning: Never call x.concat(y) when you are not
   // certain that x is an Array (x could be a string with concat method).
-  if (isArray(current)) {
+  if (Array.isArray(current)) {
     return current.concat(next);
   }
 
-  if (isArray(next)) {
+  if (Array.isArray(next)) {
     return [current].concat(next);
   }
 
diff --git a/packages/react-native-renderer/src/legacy-events/accumulateInto.js b/packages/react-native-renderer/src/legacy-events/accumulateInto.js
index d704733d9d455..35625311da88f 100644
--- a/packages/react-native-renderer/src/legacy-events/accumulateInto.js
+++ b/packages/react-native-renderer/src/legacy-events/accumulateInto.js
@@ -8,7 +8,6 @@
  */
 
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 
 /**
  * Accumulates items that must not be null or undefined into the first one. This
@@ -38,8 +37,8 @@ function accumulateInto<T>(
 
   // Both are not empty. Warning: Never call x.concat(y) when you are not
   // certain that x is an Array (x could be a string with concat method).
-  if (isArray(current)) {
-    if (isArray(next)) {
+  if (Array.isArray(current)) {
+    if (Array.isArray(next)) {
       current.push.apply(current, next);
       return current;
     }
@@ -47,7 +46,7 @@ function accumulateInto<T>(
     return current;
   }
 
-  if (isArray(next)) {
+  if (Array.isArray(next)) {
     // A bit too dangerous to mutate `next`.
     return [current].concat(next);
   }
diff --git a/packages/react-noop-renderer/src/createReactNoop.js b/packages/react-noop-renderer/src/createReactNoop.js
index 9d2c87621bcef..ce80ca3374374 100644
--- a/packages/react-noop-renderer/src/createReactNoop.js
+++ b/packages/react-noop-renderer/src/createReactNoop.js
@@ -21,7 +21,6 @@ import type {RootTag} from 'react-reconciler/src/ReactRootTags';
 
 import * as Scheduler from 'scheduler/unstable_mock';
 import {REACT_FRAGMENT_TYPE, REACT_ELEMENT_TYPE} from 'shared/ReactSymbols';
-import isArray from 'shared/isArray';
 import {
   DefaultEventPriority,
   IdleEventPriority,
@@ -605,7 +604,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     if (typeof child === 'string') {
       return child;
     }
-    if (isArray(child)) {
+    if (Array.isArray(child)) {
       if (child.length === 0) {
         return null;
       }
@@ -619,7 +618,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
       }
       return children;
     }
-    if (isArray(child.children)) {
+    if (Array.isArray(child.children)) {
       // This is an instance.
       const instance: Instance = (child: any);
       const children = childToJSX(instance.children, instance.text);
@@ -669,7 +668,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     if (children === null) {
       return null;
     }
-    if (isArray(children)) {
+    if (Array.isArray(children)) {
       return {
         $$typeof: REACT_ELEMENT_TYPE,
         type: REACT_FRAGMENT_TYPE,
@@ -688,7 +687,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     if (children === null) {
       return null;
     }
-    if (isArray(children)) {
+    if (Array.isArray(children)) {
       return {
         $$typeof: REACT_ELEMENT_TYPE,
         type: REACT_FRAGMENT_TYPE,
diff --git a/packages/react-reconciler/src/ReactChildFiber.new.js b/packages/react-reconciler/src/ReactChildFiber.new.js
index 12a693c2d2d7a..f9041ce6590b9 100644
--- a/packages/react-reconciler/src/ReactChildFiber.new.js
+++ b/packages/react-reconciler/src/ReactChildFiber.new.js
@@ -31,7 +31,6 @@ import {
   SimpleMemoComponent,
 } from './ReactWorkTags';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 import {
   warnAboutStringRefs,
   enableLazyElements,
@@ -98,6 +97,8 @@ if (__DEV__) {
   };
 }
 
+const isArray = Array.isArray;
+
 function coerceRef(
   returnFiber: Fiber,
   current: Fiber | null,
diff --git a/packages/react-reconciler/src/ReactChildFiber.old.js b/packages/react-reconciler/src/ReactChildFiber.old.js
index ad3bcdead7de6..10c4ccb4dc5be 100644
--- a/packages/react-reconciler/src/ReactChildFiber.old.js
+++ b/packages/react-reconciler/src/ReactChildFiber.old.js
@@ -11,7 +11,6 @@ import type {ReactElement} from 'shared/ReactElementType';
 import type {ReactPortal} from 'shared/ReactTypes';
 import type {Fiber} from './ReactInternalTypes';
 import type {Lanes} from './ReactFiberLane.old';
-import isArray from 'shared/isArray';
 
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import {Placement, ChildDeletion} from './ReactFiberFlags';
@@ -98,6 +97,8 @@ if (__DEV__) {
   };
 }
 
+const isArray = Array.isArray;
+
 function coerceRef(
   returnFiber: Fiber,
   current: Fiber | null,
diff --git a/packages/react-reconciler/src/ReactFiberClassComponent.new.js b/packages/react-reconciler/src/ReactFiberClassComponent.new.js
index efdd40b043188..ea1b4cb5e3c8d 100644
--- a/packages/react-reconciler/src/ReactFiberClassComponent.new.js
+++ b/packages/react-reconciler/src/ReactFiberClassComponent.new.js
@@ -29,7 +29,6 @@ import shallowEqual from 'shared/shallowEqual';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 import {REACT_CONTEXT_TYPE, REACT_PROVIDER_TYPE} from 'shared/ReactSymbols';
 
 import {resolveDefaultProps} from './ReactFiberLazyComponent.new';
@@ -75,6 +74,7 @@ import {
 } from './SchedulingProfiler';
 
 const fakeInternalInstance = {};
+const isArray = Array.isArray;
 
 // React.Component uses a shared frozen object by default.
 // We'll use it to determine whether we need to initialize legacy refs.
diff --git a/packages/react-reconciler/src/ReactFiberClassComponent.old.js b/packages/react-reconciler/src/ReactFiberClassComponent.old.js
index a34fe1d56495e..b952c24cd041d 100644
--- a/packages/react-reconciler/src/ReactFiberClassComponent.old.js
+++ b/packages/react-reconciler/src/ReactFiberClassComponent.old.js
@@ -29,7 +29,6 @@ import shallowEqual from 'shared/shallowEqual';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 import {REACT_CONTEXT_TYPE, REACT_PROVIDER_TYPE} from 'shared/ReactSymbols';
 
 import {resolveDefaultProps} from './ReactFiberLazyComponent.old';
@@ -75,6 +74,7 @@ import {
 } from './SchedulingProfiler';
 
 const fakeInternalInstance = {};
+const isArray = Array.isArray;
 
 // React.Component uses a shared frozen object by default.
 // We'll use it to determine whether we need to initialize legacy refs.
diff --git a/packages/react-reconciler/src/ReactFiberReconciler.new.js b/packages/react-reconciler/src/ReactFiberReconciler.new.js
index 4572e4d9de4ba..bbe8810ff52d7 100644
--- a/packages/react-reconciler/src/ReactFiberReconciler.new.js
+++ b/packages/react-reconciler/src/ReactFiberReconciler.new.js
@@ -34,7 +34,6 @@ import {
 } from './ReactWorkTags';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 import {enableSchedulingProfiler} from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {getPublicInstance} from './ReactFiberHostConfig';
@@ -483,9 +482,9 @@ if (__DEV__) {
     index: number,
   ) => {
     const key = path[index];
-    const updated = isArray(obj) ? obj.slice() : {...obj};
+    const updated = Array.isArray(obj) ? obj.slice() : {...obj};
     if (index + 1 === path.length) {
-      if (isArray(updated)) {
+      if (Array.isArray(updated)) {
         updated.splice(((key: any): number), 1);
       } else {
         delete updated[key];
@@ -511,12 +510,12 @@ if (__DEV__) {
     index: number,
   ) => {
     const oldKey = oldPath[index];
-    const updated = isArray(obj) ? obj.slice() : {...obj};
+    const updated = Array.isArray(obj) ? obj.slice() : {...obj};
     if (index + 1 === oldPath.length) {
       const newKey = newPath[index];
       // $FlowFixMe number or string is fine here
       updated[newKey] = updated[oldKey];
-      if (isArray(updated)) {
+      if (Array.isArray(updated)) {
         updated.splice(((oldKey: any): number), 1);
       } else {
         delete updated[oldKey];
@@ -565,7 +564,7 @@ if (__DEV__) {
       return value;
     }
     const key = path[index];
-    const updated = isArray(obj) ? obj.slice() : {...obj};
+    const updated = Array.isArray(obj) ? obj.slice() : {...obj};
     // $FlowFixMe number or string is fine here
     updated[key] = copyWithSetImpl(obj[key], path, index + 1, value);
     return updated;
diff --git a/packages/react-reconciler/src/ReactFiberReconciler.old.js b/packages/react-reconciler/src/ReactFiberReconciler.old.js
index abd5b9094c59c..c6ced2f5be5b6 100644
--- a/packages/react-reconciler/src/ReactFiberReconciler.old.js
+++ b/packages/react-reconciler/src/ReactFiberReconciler.old.js
@@ -34,7 +34,6 @@ import {
 } from './ReactWorkTags';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 import {enableSchedulingProfiler} from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {getPublicInstance} from './ReactFiberHostConfig';
@@ -483,9 +482,9 @@ if (__DEV__) {
     index: number,
   ) => {
     const key = path[index];
-    const updated = isArray(obj) ? obj.slice() : {...obj};
+    const updated = Array.isArray(obj) ? obj.slice() : {...obj};
     if (index + 1 === path.length) {
-      if (isArray(updated)) {
+      if (Array.isArray(updated)) {
         updated.splice(((key: any): number), 1);
       } else {
         delete updated[key];
@@ -511,12 +510,12 @@ if (__DEV__) {
     index: number,
   ) => {
     const oldKey = oldPath[index];
-    const updated = isArray(obj) ? obj.slice() : {...obj};
+    const updated = Array.isArray(obj) ? obj.slice() : {...obj};
     if (index + 1 === oldPath.length) {
       const newKey = newPath[index];
       // $FlowFixMe number or string is fine here
       updated[newKey] = updated[oldKey];
-      if (isArray(updated)) {
+      if (Array.isArray(updated)) {
         updated.splice(((oldKey: any): number), 1);
       } else {
         delete updated[oldKey];
@@ -565,7 +564,7 @@ if (__DEV__) {
       return value;
     }
     const key = path[index];
-    const updated = isArray(obj) ? obj.slice() : {...obj};
+    const updated = Array.isArray(obj) ? obj.slice() : {...obj};
     // $FlowFixMe number or string is fine here
     updated[key] = copyWithSetImpl(obj[key], path, index + 1, value);
     return updated;
diff --git a/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js b/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
index 85eace536ac4e..a4d0d26fcce14 100644
--- a/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
+++ b/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
@@ -14,7 +14,6 @@ import type {Request, ReactModel} from 'react-server/src/ReactFlightServer';
 import JSResourceReference from 'JSResourceReference';
 
 import hasOwnProperty from 'shared/hasOwnProperty';
-import isArray from 'shared/isArray';
 
 export type ModuleReference<T> = JSResourceReference<T>;
 
@@ -83,7 +82,7 @@ function convertModelToJSON(
 ): JSONValue {
   const json = resolveModelToJSON(request, parent, key, model);
   if (typeof json === 'object' && json !== null) {
-    if (isArray(json)) {
+    if (Array.isArray(json)) {
       const jsonArray: Array<JSONValue> = [];
       for (let i = 0; i < json.length; i++) {
         jsonArray[i] = convertModelToJSON(request, json, '' + i, json[i]);
diff --git a/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js b/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
index 0624e693cfe16..4fa871b0c4e8f 100644
--- a/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
+++ b/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
@@ -8,9 +8,9 @@
  */
 
 import type {RowEncoding, JSONValue} from './ReactFlightNativeRelayProtocol';
+
 import type {Request, ReactModel} from 'react-server/src/ReactFlightServer';
 import hasOwnProperty from 'shared/hasOwnProperty';
-import isArray from 'shared/isArray';
 import JSResourceReferenceImpl from 'JSResourceReferenceImpl';
 
 export type ModuleReference<T> = JSResourceReferenceImpl<T>;
@@ -80,7 +80,7 @@ function convertModelToJSON(
 ): JSONValue {
   const json = resolveModelToJSON(request, parent, key, model);
   if (typeof json === 'object' && json !== null) {
-    if (isArray(json)) {
+    if (Array.isArray(json)) {
       const jsonArray: Array<JSONValue> = [];
       for (let i = 0; i < json.length; i++) {
         jsonArray[i] = convertModelToJSON(request, json, '' + i, json[i]);
diff --git a/packages/react-server/src/ReactFizzServer.js b/packages/react-server/src/ReactFizzServer.js
index 75beaf0f219bf..66a6c9238ab30 100644
--- a/packages/react-server/src/ReactFizzServer.js
+++ b/packages/react-server/src/ReactFizzServer.js
@@ -51,7 +51,6 @@ import {REACT_ELEMENT_TYPE, REACT_SUSPENSE_TYPE} from 'shared/ReactSymbols';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 
 const ReactCurrentDispatcher = ReactSharedInternals.ReactCurrentDispatcher;
 
@@ -288,7 +287,7 @@ function renderNode(request: Request, task: Task, node: ReactNodeList): void {
     return;
   }
 
-  if (isArray(node)) {
+  if (Array.isArray(node)) {
     if (node.length > 0) {
       for (let i = 0; i < node.length; i++) {
         renderNode(request, task, node[i]);
diff --git a/packages/react-server/src/ReactFlightServer.js b/packages/react-server/src/ReactFlightServer.js
index 58c3a9219f644..dfbe3c55f9b64 100644
--- a/packages/react-server/src/ReactFlightServer.js
+++ b/packages/react-server/src/ReactFlightServer.js
@@ -44,7 +44,8 @@ import {
 
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
+
+const isArray = Array.isArray;
 
 type ReactJSONValue =
   | string
diff --git a/packages/react/src/ReactChildren.js b/packages/react/src/ReactChildren.js
index 9acdc068e8ea3..eb9ef5aca9ca7 100644
--- a/packages/react/src/ReactChildren.js
+++ b/packages/react/src/ReactChildren.js
@@ -10,7 +10,6 @@
 import type {ReactNodeList} from 'shared/ReactTypes';
 
 import invariant from 'shared/invariant';
-import isArray from 'shared/isArray';
 import {
   getIteratorFn,
   REACT_ELEMENT_TYPE,
@@ -111,7 +110,7 @@ function mapIntoArray(
     // so that it's consistent if the number of children grows:
     const childKey =
       nameSoFar === '' ? SEPARATOR + getElementKey(child, 0) : nameSoFar;
-    if (isArray(mappedChild)) {
+    if (Array.isArray(mappedChild)) {
       let escapedChildKey = '';
       if (childKey != null) {
         escapedChildKey = escapeUserProvidedKey(childKey) + '/';
@@ -143,7 +142,7 @@ function mapIntoArray(
   const nextNamePrefix =
     nameSoFar === '' ? SEPARATOR : nameSoFar + SUBSEPARATOR;
 
-  if (isArray(children)) {
+  if (Array.isArray(children)) {
     for (let i = 0; i < children.length; i++) {
       child = children[i];
       nextName = nextNamePrefix + getElementKey(child, i);
diff --git a/packages/react/src/ReactElementValidator.js b/packages/react/src/ReactElementValidator.js
index f9d2cbb95af14..2c14bef6c0201 100644
--- a/packages/react/src/ReactElementValidator.js
+++ b/packages/react/src/ReactElementValidator.js
@@ -23,7 +23,6 @@ import {
 } from 'shared/ReactSymbols';
 import {warnAboutSpreadingKeyToJSX} from 'shared/ReactFeatureFlags';
 import checkPropTypes from 'shared/checkPropTypes';
-import isArray from 'shared/isArray';
 
 import ReactCurrentOwner from './ReactCurrentOwner';
 import {
@@ -169,7 +168,7 @@ function validateChildKeys(node, parentType) {
   if (typeof node !== 'object') {
     return;
   }
-  if (isArray(node)) {
+  if (Array.isArray(node)) {
     for (let i = 0; i < node.length; i++) {
       const child = node[i];
       if (isValidElement(child)) {
@@ -314,7 +313,7 @@ export function jsxWithValidation(
     let typeString;
     if (type === null) {
       typeString = 'null';
-    } else if (isArray(type)) {
+    } else if (Array.isArray(type)) {
       typeString = 'array';
     } else if (type !== undefined && type.$$typeof === REACT_ELEMENT_TYPE) {
       typeString = `<${getComponentNameFromType(type.type) || 'Unknown'} />`;
@@ -353,7 +352,7 @@ export function jsxWithValidation(
     const children = props.children;
     if (children !== undefined) {
       if (isStaticChildren) {
-        if (isArray(children)) {
+        if (Array.isArray(children)) {
           for (let i = 0; i < children.length; i++) {
             validateChildKeys(children[i], type);
           }
@@ -438,7 +437,7 @@ export function createElementWithValidation(type, props, children) {
     let typeString;
     if (type === null) {
       typeString = 'null';
-    } else if (isArray(type)) {
+    } else if (Array.isArray(type)) {
       typeString = 'array';
     } else if (type !== undefined && type.$$typeof === REACT_ELEMENT_TYPE) {
       typeString = `<${getComponentNameFromType(type.type) || 'Unknown'} />`;
diff --git a/packages/react/src/jsx/ReactJSXElementValidator.js b/packages/react/src/jsx/ReactJSXElementValidator.js
index 84cf3eb2caa3b..c77b5ef6e9a6f 100644
--- a/packages/react/src/jsx/ReactJSXElementValidator.js
+++ b/packages/react/src/jsx/ReactJSXElementValidator.js
@@ -23,7 +23,6 @@ import {
 } from 'shared/ReactSymbols';
 import {warnAboutSpreadingKeyToJSX} from 'shared/ReactFeatureFlags';
 import hasOwnProperty from 'shared/hasOwnProperty';
-import isArray from 'shared/isArray';
 import {jsxDEV} from './ReactJSXElement';
 
 import {describeUnknownElementTypeFrameInDEV} from 'shared/ReactComponentStackFrame';
@@ -183,7 +182,7 @@ function validateChildKeys(node, parentType) {
     if (typeof node !== 'object') {
       return;
     }
-    if (isArray(node)) {
+    if (Array.isArray(node)) {
       for (let i = 0; i < node.length; i++) {
         const child = node[i];
         if (isValidElement(child)) {
@@ -330,7 +329,7 @@ export function jsxWithValidation(
       let typeString;
       if (type === null) {
         typeString = 'null';
-      } else if (isArray(type)) {
+      } else if (Array.isArray(type)) {
         typeString = 'array';
       } else if (type !== undefined && type.$$typeof === REACT_ELEMENT_TYPE) {
         typeString = `<${getComponentNameFromType(type.type) || 'Unknown'} />`;
@@ -367,7 +366,7 @@ export function jsxWithValidation(
       const children = props.children;
       if (children !== undefined) {
         if (isStaticChildren) {
-          if (isArray(children)) {
+          if (Array.isArray(children)) {
             for (let i = 0; i < children.length; i++) {
               validateChildKeys(children[i], type);
             }
diff --git a/packages/shared/isArray.js b/packages/shared/isArray.js
deleted file mode 100644
index 6dc19d89b21ee..0000000000000
--- a/packages/shared/isArray.js
+++ /dev/null
@@ -1,12 +0,0 @@
-/**
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @flow
- */
-
-const isArray = Array.isArray;
-
-export default isArray;