How to use param from one stream in another with RX.js?

Question

If I want to pass returned value from the first stream to second I use switchMap .

What should I use, if I want to use param from the first stream in second, but I don't want to do 2 subscribe?

this.firstStream$.subscribe(first => {
  this.secondStream$.subscribe(second => {
  // here I want to use first and second.
}

Answer 1

There's quite a few different ways to do it, depending what you are trying to accomplish. For example, there is ForkJoin:

import { of, forkJoin} from 'rxjs';

const firstObservable = of('David');
const secondObservable = of('Acosta');

forkJoin(firstObservable, secondObservable).subscribe(values => {
    const firstValue = values[0];
    const secondValue= values[1];
    console.log(firstValue);
    console.log(secondValue);
});

This waits for both to finish before emitting values. There are other operators you could use if you want one observable to emit first, such as switchMap, concat, etc.