NestJS Professional Standards & Competencies 2

Question 1

Which NestJS pattern ensures that a service's public interface remains stable while its internal implementation can change freely?

Accepted Answer

Interface-based injection tokens

Answer

Using interface-based injection tokens decouples consumers from concrete implementations, stabilizing the public contract.

Question 2

A NestJS team wants to enforce consistent error response shapes across all controllers. What is the professional best practice?

Accepted Answer

Use a global exception filter with a standardized error DTO

Answer

A global exception filter applied via APP_FILTER ensures all unhandled exceptions produce a consistent, structured response.

Question 3

When should a NestJS developer choose `forwardRef()` to resolve circular dependencies?

Accepted Answer

Only when two providers mutually depend on each other and restructuring is not feasible

Answer

`forwardRef()` is a last resort for genuine circular dependencies that cannot be resolved by restructuring the dependency graph.

Question 4

What is the professional reason to prefer `ConfigService` over `process.env` direct access inside NestJS services?

Accepted Answer

It centralizes validation, typing, and testability of environment variables

Answer

ConfigService (backed by @nestjs/config) supports schema validation, typed access, and easy mocking in unit tests.

Question 5

Which approach best supports horizontal scalability when NestJS applications need to share session state?

Accepted Answer

Externalize session state to Redis or a distributed cache

Answer

Externalizing session state to Redis allows multiple NestJS instances to share state without sticky sessions.

NestJS Practice Test