Question 1

What does an exception filter do?

Accepted Answer

Catches thrown errors and turns them into HTTP (or RPC) responses with consistent shape. Implements ExceptionFilter / @Catch. Global filters standardize API errors.

Question 2

HttpException vs domain errors — mapping strategy?

Accepted Answer

Throw domain errors in services; filter maps to HttpException/status codes at the edge. Avoid leaking ORM errors. Preserve cause for logs. Don't catch in every controller.

Question 3

Built-in vs custom filters — when custom?

Accepted Answer

Custom when you need stable error codes, i18n messages, or special logging/metrics on failures. Keep BaseExceptionFilter behaviors in mind. Test filter output contracts.

Question 4

Order of filters and @Catch specificity?

Accepted Answer

More specific @Catch(Type) preferred over broad @Catch(); registration order matters for globals. Don't register overlapping filters that fight. Document the hierarchy.

Question 5

Debugging: errors return Nest's default JSON in production unexpectedly.

Accepted Answer

Filter not registered globally, or exception type not caught; adapter differences. Ensure app.useGlobalFilters. Verify thrown types. Add e2e asserting error schema.

Question 6

Lead: unify error contracts across Nest and non-Nest services?

Accepted Answer

Shared error code catalog, problem+json or org schema, and gateway normalization. Correlate with trace IDs. Train clients on stable codes. Version the error schema.

Exception Filters NestJS Interview Questions

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