Understanding Router Service in Angular

In Angular, the Router service is critical for enabling navigation from one view to the next as users perform application tasks. When developers work with Angular, it's important to understand how Router service and Dependency Injection (DI) interact.

The quiz question mentioned was about whether Router service needs to be explicitly provided in an Angular module to use it in another component via Dependency Injection. The correct answer is 'False.'

The Router Service and Dependency Injection

In Angular, services like the Router service are provided at the root level by default. This means that they are readily available to be injected into any component without needing to be specifically declared in a module. Angular uses a hierarchical Dependency Injection system, so services are generally available to be injected into any component, irrespective of where the component is, in the component tree.

Here is an example of how you can inject the Router service in a component:

import { Router } from '@angular/router';

constructor(private router: Router) { }

In the above code, the constructor of the class has a parameter of the type Router. Hence, when Angular creates a new instance of the component, it understands from the constructor that an instance of Router is needed. Angular will then look for Router in the DI container. It will find and inject the instance of Router into the constructor.

Best Practices and Insights

The power of Angular's Dependency Injection lies in its hierarchical nature. Injectables such as services are typically provided at the level of the application root (AppModule). This makes them available throughout your app wherever they're needed.

However, Angular also gives you flexibility. You can choose to provide services at different levels - application-wide or specific to a module or a component. This is powerful in scenarios where you might want separate instances of a service for different parts of your app.

Remember, however, that providing services unnecessarily in multiple places can lead to bloated code and unexpected behavior, due to the creation of multiple service instances. Hence, a good rule of thumb is to use the root level for providing services as they are singleton at this level - which means only one instance of service is created and provided throughout the application, ensuring consistency of data and behavior.