Combine subject and observable and wait for subject to emit a value then emit observable

Question

I have one subject and observable, I want to combine them and emit the observable value and do some stuff with it after subject got new value. This code below works good but I don't want to have subscribe in subscribe

this.subject.subscribe(() => {
    this.observable.subscribe(b => {
      this.someStuffToDo(b);
    });

So the workflow is: next is invoked on subject -> observable is emitting value -> do some stuff with this value. I already tried combineLatest and zip, but it stops on the first emit of subject, or the order is wrong.

Answer 1

If you are using RxJS 6, you may consider using pipeable operators such as switchMap . The switchMap will allows you to map the observable values into the inner observable, removing the need to nest subscriptions.

this.subject
  .pipe(
    switchMap(() => this.observable),
  ).subscribe((b) => {
    this.someStuffToDo(b);
  });

And calling next() on subject will update its values.

this.subject.next(value);