What is Subject class in RxJS?

Subject is a special type of Observable in RxJS which can act as both an Observer and an Observable. It means you can use a Subject to subscribe to an Observable and also push data into it.

Here are some key points about Subject class in RxJS:

• Acts as both an Observable and an Observer
• Can multicast – meaning it can broadcast data to multiple subscribers
• Can be used to convert non-multicasted Observables and promised into multicasted Observables

Here is an example of using Subject class in RxJS:

        
            const { Subject } = rxjs;

            const subject = new Subject();

            subject.subscribe({
              next: (v) => console.log(`observerA: ${v}`)
            });

            subject.subscribe({
              next: (v) => console.log(`observerB: ${v}`)
            });

            subject.next(1);
            subject.next(2);
        
    

In this example, we create a Subject and subscribe to it with two observers. When we call `next` on the subject, both observers will receive the data.

Subject class in RxJS is commonly used for implementing event emitters, inter-component communication in Angular, and managing state in reactive applications.

It’s important to note that Subjects in RxJS can cause memory leaks if not handled properly, so it’s important to unsubscribe from them when they are no longer needed.