NestJS filters

Exception filters catch thrown exceptions and map them to HTTP responses. `@Catch()` scopes which exception types a filter handles. A global filter in `main.ts` ensures consistent error shapes.

					@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const res = ctx.getResponse<Response>();
    const status =
      exception instanceof HttpException
        ? exception.getStatus()
        : HttpStatus.INTERNAL_SERVER_ERROR;
    const body =
      exception instanceof HttpException
        ? exception.getResponse()
        : { message: 'Internal server error' };
    res.status(status).json(body);
  }
}
				

Domain exceptions can extend `HttpException` or be mapped in a custom filter. Filters run after guards, interceptors, and pipes — they are the last line for response shaping on failure.

On interviews: filters versus Express error middleware, logging in filters versus interceptors, and preserving correlation IDs.

Common pitfalls: catching everything as 500, leaking stack traces, and different error shapes per module without a global filter.

The trade-off is balancing simplicity, performance, safety, and operability — name which axis you optimized and what cost you accepted.

Checklist:

• Register a global exception filter.
• Map domain errors to HTTP status codes.
• Log server errors with context; sanitize clients.
• Use @Catch for specialized exception types.