pattern-decorator

To add logging or caching to a NestJS provider without modifying its class, wrap the provider in decorator layers that implement a shared interface, injecting new runtime behaviors while delegating execution to the base component.

The decorator pattern for adding runtime behaviors in TypeScript wraps objects in layers that share an interface, allowing you to compose responsibilities like metrics and retries around a base component without altering its class definition.

To wrap a repository with caching and logging in NestJS, define a shared interface contract and create chained decorator classes like CachedRepository and LoggedUseCase that delegate to the base object while adding functionality.

Yes, the decorator pattern requires a shared interface contract so both the base object and its wrappers can be used interchangeably throughout the application, ensuring decorators can delegate calls to the core component seamlessly.

Use the decorator pattern instead of modifying existing classes when you need to compose new responsibilities like retries or metrics at runtime while preserving the original component contracts and keeping the wrapped implementation untouched.

You can layer multiple decorators like caching and observability around a single use case by building a decorator chain where each wrapper delegates to the base component while injecting its specific functionality.