How do interceptors and exception filters divide error-handling responsibility in NestJS?

Q: How do interceptors and exception filters divide error-handling responsibility in NestJS?

// Interceptor — fixes the TYPE of the exception (runs first) @Injectable() export class DomainToHttpInterceptor implements NestInterceptor { intercept(ctx: ExecutionContext, next: CallHandler): Observable { return next.handle().pipe( catchError(err => { if (err instanceof EntityNotFoundError) throw new NotFoundException(err.message); // converted if (err instanceof QueryFailedError) throw new BadRequestException(err.message); // converted throw err; // pass unknowns to filter }), ); } } // Filter — fixes the FORMAT of the response (runs after interceptors) @Catch(HttpException) export class HttpExceptionFilter implements ExceptionFilter { catch(exception: HttpException, host: ArgumentsHost) { const res = host.switchToHttp().getResponse(); res.status(exception.getStatus()).json({ error: exception.message, timestamp: new Date().toISOString(), }); } } Interceptors (catchError) — translate exception types: EntityNotFoundError to NotFoundException. Exception filters — format the HTTP response: shape the JSON body, set headers, log errors. Interceptors run before filters in the pipeline — remap exception type first, then format the response. Use interceptors when the error type needs changing; use filters when only the response format needs changing. Always re-throw from interceptor catchError if the error is not handled — let the filter catch it.

Difficulty: 5/10

interceptors, exception filters, error handling

Interceptors via catchError() remap exception types — they convert domain or ORM errors into HttpException subclasses before the filter sees them. Exception filters shape the HTTP error response sent to the client. Interceptors fix what the exception is; filters fix how the error response looks. Interceptors run before filters in the pipeline.

Interceptor remapping vs filter formatting

Clear division of responsibility:

1
Interceptors (catchError) — translate exception types: EntityNotFoundError to NotFoundException.
2

How do interceptors and exception filters divide error-handling responsibility in NestJS?

Difficulty: 5/10

interceptors, exception filters, error handling

Interceptors via catchError() remap exception types — they convert domain or ORM errors into HttpException subclasses before the filter sees them. Exception filters shape the HTTP error response sent to the client. Interceptors fix what the exception is; filters fix how the error response looks. Interceptors run before filters in the pipeline.

Interceptor remapping vs filter formatting

Clear division of responsibility:

1
Interceptors (catchError) — translate exception types: EntityNotFoundError to NotFoundException.
2

How do interceptors and exception filters divide error-handling responsibility in NestJS?

How do interceptors and exception filters divide error-handling responsibility in NestJS?

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