Ns Uncaught Error Policy

uncaughtErrorPolicy: why 9.1 apps stopped crashing

NativeScript 9.1 changed the default handling of uncaught JS errors. The new uncaughtErrorPolicy config takes:

• 'report' (default) — log the error, fire Application.uncaughtErrorEvent, keep the app running.
• 'throw' — after reporting, rethrow natively: the app crashes like pre-9.1.

Requires runtime 9.1+ on both platforms; older runtimes ignore the key and crash as before.

// nativescript.config.ts
export default {
  id: 'org.example.app',
  uncaughtErrorPolicy: 'throw',   // TOP LEVEL ONLY — nested under ios/android it is silently ignored
  // ...
} as NativeScriptConfig;

Which one do you want?

• Shipping with a crash reporter (Sentry/Crashlytics/etc.): use 'throw'. Under 'report' the app keeps running past errors and native crash reporters see nothing — your dashboards go quiet while users hit broken states.
• Under 'report', own the reporting yourself:

import { Application } from '@nativescript/core';

Application.on(Application.uncaughtErrorEvent, (args) => {
  reportToBackend(args.error);
});

• To handle individual promise rejections instead of the global policy: globalThis.addEventListener('unhandledrejection', (e) => e.preventDefault()).

The traps

1. Placement: the key is read ONLY from the top level of nativescript.config.ts. A value nested under ios: { } or android: { } has no effect and no warning.
2. A leftover discardUncaughtJsExceptions: true defeats 'throw': it routes errors to discardedErrorEvent, skips the fatal log, and suppresses the rethrow — hiding errors from crash reporters even though you asked for 'throw'. Remove the legacy key when adopting the policy. (discardUncaughtJsExceptions: false is ignored — it does not restore crash-on-uncaught by itself.)
3. Diagnosis pattern: "our app used to crash here, now it just logs and limps" after a 9.1 upgrade is this default change, not a fix in your code. Decide the policy deliberately.

Event wiring, for completeness: the runtimes call global.__onUncaughtError → Application.uncaughtErrorEvent and global.__onDiscardedError → Application.discardedErrorEvent.

Verified 2026-08 against @nativescript/core 9.1.0-rc.3: policy values, default, top-level-only placement and the discardUncaughtJsExceptions interaction read verbatim from packages/core/config/config.interface.ts and application/application-common.ts. Crash-reporter integration behavior under each policy untested from this repo — verify with your reporter.