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I'm encountering a crash in my React Native app. The crash report from Crashlytics indicates an unhandled JavaScript exception with the following error:

Fatal Exception: RCTFatalException: Unhandled JS Exception: TypeError: Restricted in strict mode, js engine: hermes
0  CoreFoundation                 0x827cc __exceptionPreprocess
1  libobjc.A.dylib                0x172e4 objc_exception_throw
2  MyApp                          0x38a764 RCTFormatError + 167 (RCTAssert.m:167)
3  MyApp                          0x3f9354 -[RCTExceptionsManager reportFatal:stack:exceptionId:extraDataAsJSON:] + 82 (RCTExceptionsManager.mm:82)
4  MyApp                          0x3f9b74 -[RCTExceptionsManager reportException:] + 154 (RCTExceptionsManager.mm:154)
5  CoreFoundation                 0x20374 __invoking___
6  CoreFoundation                 0x1f3c4 -[NSInvocation invoke]
7  CoreFoundation                 0x94cb8 -[NSInvocation invokeWithTarget:]
8  MyApp                          0x3ba2c4 -[RCTModuleMethod invokeWithBridge:module:arguments:] + 587 (RCTModuleMethod.mm:587)
9  MyApp                          0x3bc33c facebook::react::invokeInner(RCTBridge*, RCTModuleData*, unsigned int, folly::dynamic const&, int, (anonymous namespace)::SchedulingContext) + 197 (RCTNativeModule.mm:197)
10 MyApp                          0x3bbf88 ___ZN8facebook5react15RCTNativeModule6invokeEjON5folly7dynamicEi_block_invoke + 298 (optional:298)
11 libdispatch.dylib              0x2370 _dispatch_call_block_and_release
12 libdispatch.dylib              0x40d0 _dispatch_client_callout
13 libdispatch.dylib              0xb6d8 _dispatch_lane_serial_drain
14 libdispatch.dylib              0xc1e0 _dispatch_lane_invoke
15 libdispatch.dylib              0x17258 _dispatch_root_queue_drain_deferred_wlh
16 libdispatch.dylib              0x16aa4 _dispatch_workloop_worker_thread
17 libsystem_pthread.dylib        0x4c7c _pthread_wqthread
18 libsystem_pthread.dylib        0x1488 start_wqthread

I'm trying to determine the root cause but haven't found a clear explanation yet. Here are some details about my setup and what I've tried so far:

  • React Native Version: 0.72.6
  • Crash Context: The crash is reported on Crashlytics in production after and update and I have not been able to reproduce it consistently during development.
  • Error Detail: The error message states "Restricted in strict mode". I suspect this may be related to some JavaScript code that is violating strict mode restrictions, but I'm not sure which part of the code might be causing it.
  • Investigation: I've searched for similar issues with the Hermes engine and strict mode, but haven't found a definitive answer or reproduction scenario.

Questions:

  • What could cause the "TypeError: Restricted in strict mode" error in a React Native app using Hermes? Are there known pitfalls or common coding mistakes (or library issues) that trigger this error?
  • What debugging strategies or tools can I use to isolate the problematic code since the error only appears in production?

Any insights, similar experiences, or suggestions on how to track down this issue would be greatly appreciated!

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  • Have you checked this also https://github.com/facebook/react-native/issues/34868? Commented Feb 3 at 2:06
  • Yes, I have checked, and it was unrelated to my problem. The issue was coming from an undefined value. I added 'use strict' to every component to identify the root cause. Commented Mar 4 at 21:40
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