Explain the concept of dependency injection and its role in TypeScript frameworks.

Dependency injection (DI) is a software design pattern used to manage dependencies between different components of an application. It is a concept that promotes loose coupling, modularity, and testability by allowing components to depend on abstractions rather than concrete implementations.

In the context of TypeScript frameworks, such as Angular, NestJS, or even custom applications, dependency injection plays a central role in managing the creation and resolution of dependencies within the application. Here's a more detailed explanation of the concept and its role in TypeScript frameworks:

1. Concept of Dependency Injection:
Dependency injection is based on the principle of inversion of control (IoC), which delegates the responsibility of creating and managing dependencies to an external entity, typically referred to as the "container" or "injector." The container is responsible for creating and injecting instances of dependent objects into the requesting components.
2. Dependency Inversion Principle (DIP):
Dependency injection follows the Dependency Inversion Principle, one of the SOLID principles of object-oriented design. The DIP states that high-level modules should not depend on low-level modules; both should depend on abstractions. In other words, rather than depending on concrete implementations, components should rely on interfaces or abstract classes, which allows for flexible and interchangeable implementations.
3. Role in TypeScript Frameworks:
In TypeScript frameworks, dependency injection plays a crucial role in managing the lifecycle, resolution, and wiring of components throughout the application. Here's how dependency injection is typically used in TypeScript frameworks:

a. Service Registration:
TypeScript frameworks provide mechanisms for registering services or dependencies with the container. Developers define the services they want to inject and register them in a central place, such as a module or provider configuration. This step establishes the association between abstract types or tokens and their concrete implementations.

b. Injection Decorators:
TypeScript frameworks use injection decorators (e.g., `@Injectable`, `@Inject`, `@Autowired`) to mark the dependencies that should be automatically resolved and injected into consuming components. These decorators indicate to the framework that a particular component needs a specific dependency to function correctly.

c. Dependency Resolution:
When a component is instantiated, the framework's injector or container analyzes its dependencies based on the decorators and resolves them by retrieving the registered implementations from the container. The container creates and manages the lifetime of these dependencies, ensuring that they are available when needed.

d. Hierarchical Injection:
TypeScript frameworks often support hierarchical injection, where dependencies can be resolved from parent components or modules. This allows for the composition of components and the creation of complex dependency graphs. For example, a child component can request a dependency, and the framework will traverse up the component hierarchy to find and resolve the dependency.

e. Scope and Lifetime Management:
TypeScript frameworks provide mechanisms to define the scope and lifetime of dependencies. For example, a singleton scope ensures that only a single instance of a service is created and shared across multiple components. Other scopes, such as request or transient, create a new instance of the service for each component or request, respectively.

f. Testability:
Dependency injection greatly enhances testability by facilitating the mocking or substitution of dependencies during unit testing. With DI, you can easily replace real dependencies with mock or stub implementations, enabling isolated and controlled testing of individual components.
4. Benefits of Dependency Injection:

* Loose Coupling: Dependency injection promotes loose coupling between components by removing explicit dependencies on concrete implementations. This makes components more modular, reusable, and maintainable.
* Modularity: Components become self-contained, focused on specific responsibilities, and easier to develop, test, and understand. Dependencies can be easily replaced or updated without impacting the entire system.
* Testability: By abstracting dependencies behind interfaces or abstractions, it becomes easier to isolate and mock dependencies during unit testing. Testing individual components