fix(react-is): support legacy React elements (react.element)

packages/react-is/src/ReactIs.js

@@ -12,6 +12,7 @@
 import {
   REACT_CONTEXT_TYPE,
   REACT_ELEMENT_TYPE,
+  REACT_LEGACY_ELEMENT_TYPE,
   REACT_FORWARD_REF_TYPE,
   REACT_FRAGMENT_TYPE,
   REACT_LAZY_TYPE,
@@ -42,6 +43,7 @@ export function typeOf(object: any): mixed {
     const $$typeof = object.$$typeof;
     switch ($$typeof) {
       case REACT_ELEMENT_TYPE:
+      case REACT_LEGACY_ELEMENT_TYPE:
         const type = object.type;
 
         switch (type) {
@@ -140,7 +142,8 @@ export function isElement(object: any): boolean {
   return (
     typeof object === 'object' &&
     object !== null &&
-    object.$$typeof === REACT_ELEMENT_TYPE
+    (object.$$typeof === REACT_ELEMENT_TYPE ||
+      object.$$typeof === REACT_LEGACY_ELEMENT_TYPE)
   );
 }
 export function isForwardRef(object: any): boolean {

packages/react-is/src/__tests__/ReactIs-test.js

@@ -13,6 +13,7 @@ let React;
 let ReactDOM;
 let ReactIs;
 let SuspenseList;
+let ReactSymbols;
 
 describe('ReactIs', () => {
   beforeEach(() => {
@@ -21,6 +22,7 @@ describe('ReactIs', () => {
     React = require('react');
     ReactDOM = require('react-dom');
     ReactIs = require('react-is');
+    ReactSymbols = require('shared/ReactSymbols');
 
     if (gate(flags => flags.enableSuspenseList)) {
       SuspenseList = React.unstable_SuspenseList;
@@ -116,6 +118,19 @@ describe('ReactIs', () => {
     expect(ReactIs.isElement(<React.Suspense />)).toBe(true);
   });
 
+  it('should identify legacy elements from older React versions', () => {
+    // Simulate a legacy React element with the old $$typeof symbol
+    const legacyElement = {
+      $$typeof: ReactSymbols.REACT_LEGACY_ELEMENT_TYPE,
+      type: 'div',
+      key: null,
+      ref: null,
+      props: {},
+    };
+    expect(ReactIs.isElement(legacyElement)).toBe(true);
+    expect(ReactIs.typeOf(legacyElement)).toBe(ReactIs.Element);
+  });
+
   it('should identify ref forwarding component', () => {
     const RefForwardingComponent = React.forwardRef((props, ref) => null);
     expect(ReactIs.isValidElementType(RefForwardingComponent)).toBe(true);