🔥 [🐛] Crashlytics iOS: JS crash lost on device when chaining is disabled (crashWithStackPromise exits before the report is saved) #9360

Issue

With crashlytics_javascript_exception_handler_chaining_enabled: false, an unhandled JS error on a real iOS device never reaches the Crashlytics console. The same build on the iOS simulator reports it fine, and native crashes (crash()) from the same device arrive within a minute.

Steps

1. firebase.json:

   { "react-native": { "crashlytics_javascript_exception_handler_chaining_enabled": false } }

2. In a Release build, throw from a press handler:

   import { getCrashlytics, log } from '@react-native-firebase/crashlytics';
   
   <Pressable onPress={() => {
     log(getCrashlytics(), 'about to throw');
     throw new Error('Test JS crash');
   }} />

3. Run it on an iPhone, without a debugger attached, and tap.
4. Relaunch the app and wait.

Expected: a fatal JavaScriptError: Test JS crash with the JS stack, as on the simulator.

Actual: nothing arrives: no fatal, no non-fatal, after several relaunches and more than 10 minutes. The device console shows the library recording and exiting:

-[RNFBCrashlyticsModule crashWithStackPromise:resolve:reject:] [Line 106] Crashlytics - Crash logged. Terminating app.
The app terminated with the exit code 0.

Tried twice on the device, with the same result both times. In between, a native crash() from the same install arrived, so collection, upload, and the app's Crashlytics setup all work.

Likely cause: crashWithStackPromise calls recordJavaScriptError: and then exit(0) straight away (RNFBCrashlyticsModule.mm, 26.4.0):

[self recordJavaScriptError:jsErrorDict];
ELog(@"Crashlytics - Crash logged. Terminating app.");
exit(0);

recordJavaScriptError: goes through Crashlytics' recordExceptionModel:, which saves the report asynchronously. On a device, exit(0) seems to end the process before that save completes. The faster simulator wins the race, which would explain why it works there.

Workaround: crashlytics_javascript_exception_handler_chaining_enabled: true. The same tap on the same iPhone then delivers two reports: a fatal RCTFatalException: Unhandled JS Exception: Error: … (React Native's abort), and a non-fatal JavaScriptError with the JS stack. Presumably the slower abort path gives the save time to finish. The cost is two reports per JS error, with the JS stack only in the non-fatal's frames.

Possibly related: #8898 (iOS crashes not shown in the console; closed as stale without a diagnosis).

Project Files

Javascript

{
  "dependencies": {
    "@react-native-firebase/analytics": "26.4.0",
    "@react-native-firebase/app": "26.4.0",
    "@react-native-firebase/crashlytics": "26.4.0",
    "@react-native-firebase/remote-config": "26.4.0",
    "expo": "~57.0.25",
    "react": "19.2.3",
    "react-native": "0.86.3"
  }
}

{
  "react-native": {
    "crashlytics_javascript_exception_handler_chaining_enabled": false,
    "crashlytics_debug_enabled": false
  }
}

iOS

# Expo prebuild (CNG). Relevant config:
#   ["@react-native-firebase/app", { "ios": { "disableSPM": true } }]
#   "@react-native-firebase/crashlytics"
#   ["@react-native-firebase/analytics", { "ios": { "withoutAdIdSupport": true } }]
#   ["expo-build-properties", { "ios": { "useFrameworks": "static",
#     "forceStaticLinking": ["RNFBApp","RNFBAnalytics","RNFBCrashlytics","RNFBRemoteConfig"] } }]
# Firebase iOS SDK resolved by CocoaPods: 12.18.0. New Architecture, Hermes.

// Swift AppDelegate from Expo SDK 57; the RNFB config plugin adds FirebaseApp.configure()
// in didFinishLaunchingWithOptions.

Android

// N/A (iOS only)

// N/A

// N/A

// N/A

<!-- N/A -->

Environment

React Native 0.86.3 (New Architecture, Hermes), Expo SDK 57.0.25
Xcode 27.0 (27A266a), macOS 26.6.1
Device: iPhone 16e, iOS 26.7 (fails). Simulator: iPhone 17, iOS 27.0 (works)