NestJS Professional Standards & Competencies 4

Question 1

A NestJS API receives file uploads. Which professional practice minimizes security risk?

Accepted Answer

Validate file type via MIME type and magic bytes, enforce size limits, and store files outside the web root

Answer

Validating MIME type, enforcing size limits, and using secure storage prevents path traversal, malware uploads, and resource exhaustion.

Question 2

What is the correct NestJS pattern for running expensive initialization logic once before the application starts accepting requests?

Accepted Answer

Implement `onModuleInit()` or `onApplicationBootstrap()` in the relevant provider

Answer

onModuleInit() and onApplicationBootstrap() lifecycle hooks provide deterministic initialization points before the app is fully ready.

Question 3

Which NestJS technique allows different environments (dev, staging, prod) to use different provider implementations without changing business logic?

Accepted Answer

Use dynamic modules or conditional providers based on environment variables

Answer

Dynamic modules and conditional provider registration allow swapping implementations at bootstrap time based on the environment.

Question 4

A team discovers that a NestJS interceptor is adding latency to every request. What is the professional debugging approach?

Accepted Answer

Use NestJS performance hooks or APM tooling to measure interceptor execution time and identify the bottleneck

Answer

Measuring with APM or custom timing identifies the specific interceptor and operation causing latency before making changes.

Question 5

What is the professional standard for handling database transactions that span multiple repository operations in NestJS with TypeORM?

Accepted Answer

Use a DataSource QueryRunner or the @Transaction() pattern to wrap operations in a single atomic transaction

Answer

QueryRunner-based transactions guarantee atomicity across multiple operations, preventing partial writes on failure.

NestJS Practice Test