Restringimento degli errori intercettati (unknown o Error)

Benvenuto

Modifica in TS 4.0

// err is now: unknown
try { doSomething(); }
catch (err) {
  // err.message; // Error — cannot access on unknown
}

Restringimento con instanceof

catch (err) {
  if (err instanceof Error) {
    console.error(err.message, err.stack);
  } else {
    console.error('Unknown error:', String(err));
  }
}

Type guard isError

function isError(e: unknown): e is Error {
  return e instanceof Error;
}
catch (e) {
  if (isError(e)) console.error(e.message);
}

Restringimento degli errori personalizzati

catch (err) {
  if (err instanceof NetworkError) { /* retry */ }
  else if (err instanceof AuthError) { /* redirect */ }
  else if (err instanceof Error) { /* generic */ }
  else throw err;
}

useUnknownInCatchVariables

{ "compilerOptions": { "useUnknownInCatchVariables": true } }

Errori stringa

catch (err) {
  const message = err instanceof Error ? err.message : String(err);
  console.error(message);
}

Helper typed throw

function throwErr(msg: string, code = 500): never {
  const e: AppError = Object.assign(new Error(msg), { statusCode: code });
  throw e;
}

Rilanciare errori unknown

catch (err) {
  if (err instanceof KnownError) handle(err);
  else throw err; // propagate unknowns
}

Error boundary in React

componentDidCatch(error: unknown, info: ErrorInfo) {
  if (error instanceof Error) logError(error.message);
}

Testare gli errori catturati

test('catches errors', async () => {
  jest.spyOn(api, 'fetch').mockRejectedValue(new NetworkError());
  const result = await safeRun();
  expect(result.ok).toBe(false);
});

Verifica rapida

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