Subject and Behavior Subject in Angular

In Angular, a Subject is a special type of Observable that allows values to be multicasted to many Observers. This means that multiple subscribers can listen to a Subject and receive the same values emitted by it. On the other hand, a Behavior Subject is a type of Subject that has a “current value” which can be accessed by subscribers. When a new subscriber subscribes to a Behavior Subject, it will immediately receive the “current value” of the Subject.

Subjects are commonly used for event handling and state management in Angular applications. They are particularly useful for broadcasting events and sharing data between different parts of the application. Behavior Subjects, in particular, are often used to manage the state of a component or service by providing a single source of truth for the current state.

Creating a Subject and Behavior Subject

Creating a Subject and Behavior Subject in Angular is simple. You can import the required classes from the rxjs library and then instantiate them in your component or service.

“`typescript
import { Subject, BehaviorSubject } from ‘rxjs’;

// Creating a Subject
const mySubject = new Subject();

// Creating a Behavior Subject
const myBehaviorSubject = new BehaviorSubject(‘initial value’);
“`

Subscribing to a Subject and Behavior Subject

Once you have created a Subject or Behavior Subject, you can subscribe to it in order to receive the values emitted by it. Subscribing to a Subject or Behavior Subject is similar to subscribing to a regular Observable.

“`typescript
// Subscribing to a Subject
mySubject.subscribe(
(value) => {
console.log(‘Received value: ‘, value);
}
);

// Subscribing to a Behavior Subject
myBehaviorSubject.subscribe(
(value) => {
console.log(‘Received value: ‘, value);
}
);
“`

Emmiting values with a Subject and Behavior Subject

To emit a new value with a Subject or Behavior Subject, you can simply call the next() method on the subject and pass in the value that you want to emit.

“`typescript
// Emitting a value with a Subject
mySubject.next(‘new value’);

// Emitting a value with a Behavior Subject
myBehaviorSubject.next(‘new value’);
“`

Overall, Subjects and Behavior Subjects are powerful tools for managing state and broadcasting events in Angular. They are widely used in Angular applications and can help improve the reactivity and efficiency of the application.