Harden window and navigator global property descriptors

packages/react-native/Libraries/Core/setUpGlobals.js

@@ -15,14 +15,19 @@
  * Sets up global variables for React Native.
  * You can use this module directly, or just require InitializeCore.
  */
-if (global.window === undefined) {
+if (globalThis.window === undefined) {
   // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
-  global.window = global;
+  Object.defineProperty(globalThis, 'window', {
+    value: globalThis,
+    configurable: false,
+    enumerable: true,
+    writable: false,
+  });
 }
 
-if (global.self === undefined) {
+if (globalThis.self === undefined) {
   // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
-  global.self = global;
+  globalThis.self = globalThis;
 }
 
 // Set up process

packages/react-native/Libraries/Core/setUpNavigator.js

@@ -15,7 +15,12 @@ const {polyfillObjectProperty} = require('../Utilities/PolyfillFunctions');
 const navigator = global.navigator;
 if (navigator === undefined) {
   // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
-  global.navigator = {product: 'ReactNative'};
+  Object.defineProperty(global, 'navigator', {
+    value: {product: 'ReactNative'},
+    configurable: true,
+    enumerable: true,
+    writable: false,
+  });
 } else {
   // see https://github.com/facebook/react-native/issues/10881
   polyfillObjectProperty(navigator, 'product', () => 'ReactNative');

packages/react-native/src/private/setup/__tests__/setUpDefaultReactNativeEnvironment-Globals-itest.js

@@ -14,6 +14,25 @@ import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
 declare var PerformanceObserverEntryList: unknown;
 declare var EventCounts: unknown;
 
+function expectGlobalDescriptorToMatch(
+  name: string,
+  expected: {
+    enumerable: boolean,
+    configurable: boolean,
+    writable: boolean,
+  },
+) {
+  const descriptor = Object.getOwnPropertyDescriptor(globalThis, name);
+  if (descriptor == null) {
+    throw new Error(`Expected globalThis.${name} to be defined`);
+  }
+  expect({
+    enumerable: descriptor.enumerable,
+    configurable: descriptor.configurable,
+    writable: descriptor.writable,
+  }).toEqual(expected);
+}
+
 describe('setUpDefaultReactNativeEnvironment (globals)', () => {
   describe('global object', () => {
     it('should be exposed as globalThis, global, window and self', () => {
@@ -23,6 +42,56 @@ describe('setUpDefaultReactNativeEnvironment (globals)', () => {
     });
   });
 
+  describe('property descriptors', () => {
+    it('should define window as enumerable but not configurable or writable', () => {
+      expectGlobalDescriptorToMatch('window', {
+        enumerable: true,
+        configurable: false,
+        writable: false,
+      });
+    });
+
+    it('should define self as configurable, enumerable and writable', () => {
+      expectGlobalDescriptorToMatch('self', {
+        enumerable: true,
+        configurable: true,
+        writable: true,
+      });
+    });
+
+    it('should define navigator as configurable and enumerable but not writable', () => {
+      expectGlobalDescriptorToMatch('navigator', {
+        enumerable: true,
+        configurable: true,
+        writable: false,
+      });
+    });
+
+    it('should define Infinity as not configurable, writable or enumerable', () => {
+      expectGlobalDescriptorToMatch('Infinity', {
+        enumerable: false,
+        configurable: false,
+        writable: false,
+      });
+    });
+
+    it('should define NaN as not configurable, writable or enumerable', () => {
+      expectGlobalDescriptorToMatch('NaN', {
+        enumerable: false,
+        configurable: false,
+        writable: false,
+      });
+    });
+
+    it('should define undefined as not configurable, writable or enumerable', () => {
+      expectGlobalDescriptorToMatch('undefined', {
+        enumerable: false,
+        configurable: false,
+        writable: false,
+      });
+    });
+  });
+
   describe('environment', () => {
     it('should provide process.env.NODE_ENV', () => {
       expect(process.env.NODE_ENV).toBe('development');