Questions
6 of 11
1What is a provider in NestJS?
2What are the different forms of custom provider syntax in NestJS?
3How does NestJS handle async providers and what problem do they solve?
4What are provider scopes in NestJS and when would you change the default?
5How do you resolve a circular dependency between two providers in NestJS?
6Walk through all four custom provider types: useClass, useValue, useFactory, useExisting.
7How do you create a multi-provider pattern in NestJS to inject multiple implementations for the same token?
8How does an async provider work in NestJS and what guarantees does it give?
9What is the shorthand provider syntax in NestJS and what does it expand to?
10What is the difference between useExisting and useClass when aliasing a provider in NestJS?
11How do you make a provider accessible across the entire module graph using ModuleRef.get() with strict: false?
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06 / 11

Walk through all four custom provider types: useClass, useValue, useFactory, useExisting.

useClass provides a class to be instantiated. useValue provides a static value or mock object. useFactory provides the return value of a factory function that supports async and dependency injection via the inject array. useExisting creates an alias so two tokens resolve to the same singleton instance.

All four custom provider forms
Key rules for each form:
  1. 1

    useClass — NestJS instantiates the class and manages its lifecycle.

  2. 2

    useValue — the value is used as-is; no instantiation or lifecycle management.

  3. 3

    useFactory — the inject array lists tokens resolved and passed as factory arguments in order.

  4. 4

    useFactory supports async; NestJS awaits the returned Promise before the app starts.

  5. 5

    useExisting — does NOT create a new instance; resolves the existing singleton for the referenced token.