What is the cause option on HttpException and how should you use it for error tracing?

0-2 years experience

1. 1If you throw new HttpException('Invalid input', HttpStatus.BAD_REQUEST, { cause: new ValidationError() }), what will NestJS include in the response and how can you later retrieve the original ValidationError?
2. 2You need to log the stack trace of an underlying error when returning a 500 error from a controller. How would you use the cause option on HttpException to achieve that?
3. 3What happens if you omit the cause option when wrapping another error in HttpException? Will the original error be lost for logging?

2-5 years experience

1. 1During a recent feature you wrapped a database error inside an HttpException using the cause option, but the logs only show the HttpException message. What could be misconfigured in your NestJS setup that prevents the cause from being logged?
2. 2You have a global exception filter that formats error responses. How would you modify it to include information from the cause property of HttpException without exposing sensitive details?
3. 3Explain why using the cause option is preferable to concatenating error messages when you need to trace errors across async service calls.

5-8 years experience

1. 1In a high‑traffic microservice, you need to propagate error context across several layers (service, repository, external API). How would you design the error handling strategy using HttpException's cause to maintain traceability while keeping performance overhead low?
2. 2Your team is migrating from custom error classes to NestJS HttpException with cause. What edge cases (e.g., circular causes, serialization) must you watch for and how would you mitigate them?
3. 3When integrating with a logging platform that expects a flat error object, how would you extract and flatten the nested cause chain from HttpException without losing stack information?

8+ years experience

1. 1Across multiple NestJS services, you want a unified error‑tracking convention that leverages HttpException's cause. How would you define a shared library or pattern that enforces consistent use, supports correlation IDs, and integrates with centralized observability tools?
2. 2Consider a legacy monolith where errors are thrown as plain strings. What migration path would you propose to adopt HttpException with cause, ensuring backward compatibility and minimal disruption to existing error handling middleware?
3. 3At scale, storing full error cause chains can increase log volume. How would you design a policy for truncating or sampling cause information while still enabling root‑cause analysis for critical incidents?