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fix: guard against duplicate Fusebox DevTools dispatcher initialization#56316

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am6737 wants to merge 1 commit intofacebook:mainfrom
am6737:fix-fusebox-devtools-hmr-guard
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fix: guard against duplicate Fusebox DevTools dispatcher initialization#56316
am6737 wants to merge 1 commit intofacebook:mainfrom
am6737:fix-fusebox-devtools-hmr-guard

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@am6737 am6737 commented Apr 3, 2026

Summary:

When using Expo dev client, switching the app from background to foreground can cause TypeError: property is not writable in setUpFuseboxReactDevToolsDispatcher.js .

This issue only affects development builds - production builds are not affected because:

  1. setUpFuseboxReactDevToolsDispatcher.js is only loaded in DEV mode
  2. Metro HMR is not available in production builds
    The issue occurs because Metro HMR may invalidate module cache during foreground transitions, causing setUpDefaultReactNativeEnvironment to be re-executed and its initialized guard to be reset. This leads to Object.defineProperty on FUSEBOX_REACT_DEVTOOLS_DISPATCHER running twice with configurable: false and writable: false , which throws an error.

Root cause:

  1. App goes to background → Metro HMR WebSocket disconnects
  2. App returns to foreground → WebSocket reconnects
  3. Metro sends "update" message to sync state (even if no code changed)
  4. HMR client re-evaluates modules via eval()
  5. setUpDefaultReactNativeEnvironment.js is re-evaluated, initialized flag is reset
  6. setUpFuseboxReactDevToolsDispatcher.js runs again
  7. Object.defineProperty fails because property already exists with configurable: false
    The fix makes the property definition idempotent by checking if it already exists before defining it.

error log

ERROR  ExceptionsManager should be set up after React DevTools to avoid console.error arguments mutation 
Code: construct.js
  2 | var setPrototypeOf = require("./setPrototypeOf.js");
  3 | function _construct(t, e, r) {
> 4 |   if (isNativeReflectConstruct()) return Reflect.construct.apply(null, arguments);
    |                                                                 ^
  5 |   var o = [null];
  6 |   o.push.apply(o, e);
  7 |   var p = new (t.bind.apply(t, o))();
Call Stack
  construct (xxx/<native>)
  apply (xxx/<native>)
  _construct (xxx/node_modules/@babel/runtime/helpers/construct.js:4:65)
  Wrapper (xxx/node_modules/@babel/runtime/helpers/wrapNativeSuper.js:15:14)
  construct (xxx/<native>)
  _callSuper (xxx/node_modules/@babel/runtime/helpers/callSuper.js:5:108)
  NamelessError (xxx/node_modules/@expo/metro-runtime/src/metroServerLogs.native.ts:102:20)
  captureCurrentStack (xxx/node_modules/@expo/metro-runtime/src/metroServerLogs.native.ts:106:27)
  HMRClient.log (xxx/node_modules/@expo/metro-runtime/src/metroServerLogs.native.ts:39:79)
  console.level (xxx/node_modules/react-native/Libraries/Core/setUpDeveloperTools.js:41:24)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Core/setUpReactDevTools.js:26:18)
  setUpDefaltReactNativeEnvironment (node_modules/expo/node_modules/react-native/src/private/setup/setUpDefaultReactNativeEnvironment.js:28:12)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Core/InitializeCore.js:31:78)
  <global> (node_modules/expo/node_modules/react-native/Libraries/ReactPrivate/ReactNativePrivateInitializeCore.js:11)
  <anonymous> (node_modules/expo/node_modules/react-native/Libraries/Renderer/implementations/ReactFabric-dev.js:13872:12)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Renderer/implementations/ReactFabric-dev.js:16837:4)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Renderer/shims/ReactFabric.js:22:24)
  renderElement (node_modules/expo/node_modules/react-native/Libraries/ReactNative/RendererImplementation.js:37:12)
  renderApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/renderApplication.js:102:25)
  runnables.appKey (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:89:22)
  runApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:178:20)
 ERROR  [TypeError: property is not writable] 
Code: setUpFuseboxReactDevToolsDispatcher.js
  106 | }
  107 |
> 108 | Object.defineProperty(global, '__FUSEBOX_REACT_DEVTOOLS_DISPATCHER__', {
      |                      ^
  109 |   value: FuseboxReactDevToolsDispatcher,
  110 |   configurable: false,
  111 |   enumerable: false,
Call Stack
  defineProperty (xxx/<native>)
  <global> (node_modules/expo/node_modules/react-native/src/private/devsupport/rndevtools/setUpFuseboxReactDevToolsDispatcher.js:108:22)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Core/setUpReactDevTools.js:34:10)
  setUpDefaltReactNativeEnvironment (node_modules/expo/node_modules/react-native/src/private/setup/setUpDefaultReactNativeEnvironment.js:28:12)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Core/InitializeCore.js:31:78)
  <global> (node_modules/expo/node_modules/react-native/Libraries/ReactPrivate/ReactNativePrivateInitializeCore.js:11)
  <anonymous> (node_modules/expo/node_modules/react-native/Libraries/Renderer/implementations/ReactFabric-dev.js:13872:12)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Renderer/implementations/ReactFabric-dev.js:16837:4)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Renderer/shims/ReactFabric.js:22:24)
  renderElement (node_modules/expo/node_modules/react-native/Libraries/ReactNative/RendererImplementation.js:37:12)
  renderApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/renderApplication.js:102:25)
  runnables.appKey (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:89:22)
  runApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:178:20)
 ERROR  [TypeError: Cannot read property 'default' of undefined] 
Code: RendererImplementation.js
  35 | }): void {
  36 |   if (useFabric) {
> 37 |     require('../Renderer/shims/ReactFabric').default.render(
     |                                             ^
  38 |       element,
  39 |       rootTag,
  40 |       null,
Call Stack
  renderElement (node_modules/expo/node_modules/react-native/Libraries/ReactNative/RendererImplementation.js:37:45)
  renderApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/renderApplication.js:102:25)
  runnables.appKey (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:89:22)
  runApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:178:20)
 ERROR  [TypeError: property is not writable] 
Code: setUpFuseboxReactDevToolsDispatcher.js
  106 | }
  107 |
> 108 | Object.defineProperty(global, '__FUSEBOX_REACT_DEVTOOLS_DISPATCHER__', {
      |                      ^
  109 |   value: FuseboxReactDevToolsDispatcher,
  110 |   configurable: false,
  111 |   enumerable: false,
Call Stack
  defineProperty (xxx/<native>)
  <global> (node_modules/expo/node_modules/react-native/src/private/devsupport/rndevtools/setUpFuseboxReactDevToolsDispatcher.js:108:22)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Core/setUpReactDevTools.js:34:10)
  setUpDefaltReactNativeEnvironment (node_modules/expo/node_modules/react-native/src/private/setup/setUpDefaultReactNativeEnvironment.js:28:12)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Core/InitializeCore.js:31:78)
  <global> (node_modules/expo/node_modules/react-native/Libraries/ReactPrivate/ReactNativePrivateInitializeCore.js:11)
  <anonymous> (node_modules/expo/node_modules/react-native/Libraries/Renderer/implementations/ReactFabric-dev.js:13872:12)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Renderer/implementations/ReactFabric-dev.js:16837:4)
  <global> (node_modules/expo/node_modules/react-native/Libraries/Renderer/shims/ReactFabric.js:22:24)
  renderElement (node_modules/expo/node_modules/react-native/Libraries/ReactNative/RendererImplementation.js:37:12)
  renderApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/renderApplication.js:102:25)
  runnables.appKey (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:89:22)
  runApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:178:20)
 ERROR  [TypeError: Cannot read property 'default' of undefined] 
Code: RendererImplementation.js
  35 | }): void {
  36 |   if (useFabric) {
> 37 |     require('../Renderer/shims/ReactFabric').default.render(
     |                                             ^
  38 |       element,
  39 |       rootTag,
  40 |       null,
Call Stack
  renderElement (node_modules/expo/node_modules/react-native/Libraries/ReactNative/RendererImplementation.js:37:45)
  renderApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/renderApplication.js:102:25)
  runnables.appKey (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:89:22)
  runApplication (node_modules/expo/node_modules/react-native/Libraries/ReactNative/AppRegistryImpl.js:178:20)

Changelog:

[GENERAL] [FIXED] - Guard against duplicate Fusebox DevTools dispatcher initialization during HMR reconnection

Test Plan:

  • Applied the fix as a patch to the affected app. After patching, the error no longer occurs during background/foreground transitions.

@am6737
fix: guard against duplicate Fusebox DevTools dispatcher initialization
0caa186 
When using Expo dev client, switching the app from background to foreground
can cause 'TypeError: property is not writable' in setUpFuseboxReactDevToolsDispatcher.

The issue occurs because Metro HMR may invalidate module cache during
foreground transitions, causing setUpDefaultReactNativeEnvironment to be
re-executed and its initialized guard to be reset. This leads to
Object.defineProperty on __FUSEBOX_REACT_DEVTOOLS_DISPATCHER__ running twice.

The fix is to make the property definition idempotent by checking if it
already exists before defining it.
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@meta-cla meta-cla bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Apr 3, 2026
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