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Diagnostics Hook ​

Problem ​

Implement diagnostics hook in a production-friendly way with @vielzeug/i18nit while keeping setup and cleanup explicit.

Runnable Example ​

The snippet below is copy-paste runnable in a TypeScript project with @vielzeug/i18nit installed.

ts
const i18nWithDiagnostics = createI18n({
  locale: 'en',
  loaders: {
    fr: () => fetch('/api/locales/fr').then((r) => r.json()),
  },
  onDiagnostic: (event) => {
    if (event.kind === 'loader-error') {
      console.warn('Loader failed:', event.locale, event.error);
    } else {
      console.error('Subscriber failed:', event.error);
    }
  },
});

Expected Output ​

  • The example runs without type errors in a standard TypeScript setup.
  • The main flow produces the behavior described in the recipe title.

Common Pitfalls ​

  • Forgetting cleanup/dispose calls can leak listeners or stale state.
  • Skipping explicit typing can hide integration issues until runtime.
  • Not handling error branches makes examples harder to adapt safely.