TOPIC OVERVIEW

NestJS/Dependency Injection

Let NestJS create and connect your application's dependencies instead of wiring everything together manually.

18 QuestionsAdvancedHigh Priority ~12 min read

Dependency injection means a class does not have to create the objects it depends on itself. Instead, NestJS's dependency injection container creates those objects and provides them where they are needed.

For example, a UsersService can receive a database repository or another service through its constructor without manually creating either one. This reduces tight coupling and makes components easier to replace, test, and maintain.

What you'll walk away knowing

What dependency injection means

How NestJS's dependency injection container works

How constructor injection connects dependencies

Why dependency injection improves testing and maintainability

1What is property-based injection in NestJS and when should you use it?Intermediate 2What is the correct architectural solution for circular dependencies beyond forwardRef()?Advanced 3How does moduleRef.resolve() work with scoped providers and what is ContextIdFactory used for?Intermediate 4What is LazyModuleLoader in NestJS and how does it differ from standard DI?Intermediate 5How do you replace a provider in a NestJS test module using overrideProvider()?Intermediate 6What role does reflect-metadata play in NestJS DI?Intermediate 7What is a circular dependency in NestJS and how does it manifest at runtime?Intermediate 8What are the three provider scopes in NestJS and when is each appropriate?Intermediate 9What is a DI token and what types can be used as tokens in NestJS?Intermediate 10How do you implement the Strategy pattern using NestJS DI?Intermediate 11How does forwardRef() solve circular dependencies in NestJS and how does it work internally?Advanced 12When do you need @Inject(TOKEN) vs plain constructor injection in NestJS?Intermediate 13What happens to REQUEST-scoped providers during WebSocket connections or microservice message handling in NestJS?Intermediate 14What is the difference between moduleRef.get() and moduleRef.resolve() in NestJS?Intermediate 15What is the difference between Dependency Injection (DI) and Inversion of Control (IoC)?Intermediate 16What is scope propagation in NestJS and why can it impact performance?Intermediate 17How do you pass a custom REQUEST object to a REQUEST-scoped provider for queues or CRON jobs in NestJS?Advanced 18How do you inject the raw HTTP request object inside a REQUEST-scoped provider in NestJS?Intermediate 19How does NestJS resolve constructor injection at runtime?Intermediate 20How do you detect and debug circular dependency errors in large NestJS projects?Intermediate 21How do you write a unit test for a NestJS service that has injected dependencies?Intermediate 22What is ModuleRef in NestJS and when would you use it?Intermediate 23What does @Optional() decorator do in NestJS?Intermediate 24What is Inversion of Control (IoC) and how does NestJS implement it?Intermediate

All Topics

1

Dependency Injection

2

Request Lifecycle

Exception Handling

3

4

Database and ORM

5

Authentication and Authorization

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