Heading 1: Understanding Angular Injector
Angular is a popular framework for building web applications and has a robust dependency injection system built-in. This dependency injection system is managed by the Angular Injector, which is responsible for creating and providing instances of the required objects.
In angular, an injector is a container which contains a set of service instances that can be injected across the application. It is responsible for creating instances of the required objects and providing these instances when required by other components in the application.
In simple terms, every component, service, and directive in the Angular application gets instantiated via the injector. The injector’s primary goal is to make sure all necessary objects are available within the scope of the application.
In this article, we’ll discuss everything you need to know about Angular Injector.
Heading 2: How Angular Injector Works
Angular Injector is part of the Angular core and provides a way to create and manage dependencies between different components in your application. It does this by creating a dependency injection graph, where each node represents a dependency and each edge represents the relationship between them.
When a component or service needs a dependency, it asks the injector to provide it. The injector looks up the dependency in the graph and determines what to do based on the type of dependency.
There are three types of dependencies in Angular:
1. Value: A simple value, such as a string or number.
2. Factory: A function that returns a value.
3. Service: An object with methods that can be used throughout the application.
The Injector resolves dependencies recursively so that when a component requests a service, it will resolve any dependencies that service may have.
Here’s an example:
“`
class Logger {
log(message: string) {
console.log(message);
}
}
class ApiService {
constructor(private logger: Logger) {}
getProducts() {
this.logger.log(‘getProducts called’);
// code to fetch products
}
}
class AppComponent {
constructor(private api: ApiService) {}
ngOnInit() {
this.api.getProducts();
}
}
“`
In this example, the `AppComponent` needs an instance of the `ApiService`. The `ApiService` needs an instance of the `Logger`. When the `AppComponent` requests an instance of the `ApiService`, the injector creates an instance of the `Logger`, then an instance of the `ApiService` with the instance of the `Logger` injected into it.
Heading 3: Configuring Dependency Injection
Angular provides several ways to configure dependency injection. The most common way is through the `@Injectable` decorator.
The `@Injectable` decorator tells Angular that a class can be injected with dependencies. When the Angular Compiler sees an `@Injectable` decorator, it generates metadata about the class and its dependencies. This metadata is used by the Injector to create instances of the class and its dependencies.
Here’s an example:
“`
@Injectable({
providedIn: ‘root’
})
class Logger {
log(message: string) {
console.log(message);
}
}
“`
In this example, the `Logger` class is marked with the `@Injectable` decorator and has its `providedIn` property set to `’root’`. This tells Angular to provide a single instance of the `Logger` for the entire application.
Angular provides several other ways to configure dependency injection, including constructor injection, provider-based injection, and module-based injection.
Heading 4: FAQs
1. What is dependency injection?
Dependency injection is a technique for managing object dependencies. In an Angular application, dependency injection involves creating and managing instances of objects that are required by other objects.
2. What is the role of Angular Injector?
The Angular Injector is responsible for creating and providing instances of the required objects. It creates a dependency injection graph, where each node represents a dependency and each edge represents the relationship between them.
3. What are the types of dependencies in Angular?
There are three types of dependencies in Angular: value, factory, and service.
4. How do you configure dependency injection in Angular?
Angular provides several ways to configure dependency injection, including the `@Injectable` decorator, constructor injection, provider-based injection, and module-based injection.
5. What is the difference between constructor injection and provider-based injection?
In constructor injection, the dependencies are provided as constructor parameters, while in provider-based injection, the dependencies are provided in a separate provider object.
Heading 5: Conclusion
Angular Injector is a powerful feature in Angular that allows for the easy management of object dependencies. It simplifies the process of creating and providing instances of the required objects, making the development process faster and more efficient. Understanding how the Angular Injector works and how to configure it is an essential part of developing Angular applications.