Questions
7 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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07 / 11

How do you create a multi-provider pattern in NestJS to inject multiple implementations for the same token?

NestJS does not natively support multi-providers like Angular, but the same result is achieved with a factory provider that aggregates all implementations into an array or map and exposes them under a single token.

Multi-provider pattern using a factory
Advantages of this approach:
  1. 1

    Adding a new notifier only requires registering it as a provider and adding it to the factory — no changes to NotificationService.

  2. 2

    Each implementation is a singleton provider and can inject its own dependencies.

  3. 3

    The array token is easy to mock in tests with a simple useValue array.

  4. 4

    Works for any interface-based polymorphism scenario: validators, event handlers, middleware chains.