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Testing

Learn how to safely test your error handling setup and simulate crashes in development.

Simulating JavaScript Errors​

To test your JS exception handler, throw an error in your app:

import { setJSExceptionHandler } from 'react-native-global-exception-handler';

setJSExceptionHandler((error, isFatal) => {
  console.log('JS Exception:', error, isFatal);
}, true);

// Somewhere in your code
throw new Error('Test JS Error');

Simulating Native Crashes​

Use the built-in simulateNativeCrash function to trigger native crashes for testing. Warning: This will crash your app.

import { simulateNativeCrash, CrashType } from 'react-native-global-exception-handler';

// Simulate a standard NSException (iOS) or equivalent (Android)
simulateNativeCrash(CrashType.nsexception);

// Simulate other crash types
simulateNativeCrash(CrashType.array_bounds);
simulateNativeCrash(CrashType.memory_access);

Available Crash Types: See the full list in the CrashType section of the API Reference.

Platform Support​

  • Works only on iOS and Android (not web)
  • Some crash types may only be available on one platform

Best Practices​

  • Only use crash simulation in development or QA builds
  • Guard test code with __DEV__ to avoid accidental production crashes:
if (__DEV__) {
  global.simulateCrash = () => {
    simulateNativeCrash('nsexception');
  };
}
  • Remove or disable test crash triggers before releasing your app

Development Mode vs Production Mode​

Important: Native exception handlers behave differently in dev vs production:

  • Development Mode: Native exception handler is NOT active - you'll see the Red Screen
  • Production/Bundle Mode: Native exception handler is active - your handler will be called

To test native exception handling:

  1. Build a production/release bundle:

    # iOS
    npx react-native run-ios --configuration Release

    # Android
    npx react-native run-android --variant=release

  2. Or disable dev mode in your code:

    // Temporarily force production behavior for testing
    if (__DEV__) {
      console.log('Testing native handler in dev mode');
      // Note: Native handler still won't work, need release build
    }

Why? The Red Screen in development mode is designed to help you debug. Native exception handlers only activate in production builds to avoid interfering with React Native's development tools.

Testing Analytics Integration​

To verify that errors are sent to your analytics service:

  1. Trigger a JS or native crash
  2. Check your analytics dashboard for the error event
  3. Use local logging or AsyncStorage to confirm handler execution

Example: Verifying Handler Execution​

import AsyncStorage from '@react-native-async-storage/async-storage';

setNativeExceptionHandler(async (errorString) => {
  // Log locally for verification
  await AsyncStorage.setItem('lastNativeCrash', JSON.stringify({
    error: errorString,
    timestamp: new Date().toISOString()
  }));
  
  // Send to analytics
  reportToAnalytics(errorString);
});

// Later, check if handler was called
AsyncStorage.getItem('lastNativeCrash').then(data => {
  if (data) {
    console.log('Last crash:', JSON.parse(data));
  }
});

Troubleshooting​

See Troubleshooting