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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

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

All Topics

1

Dependency Injection

2

Request Lifecycle

Exception Handling

3

4

Database and ORM

5

Authentication and Authorization