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.
}

You can use `first` inside `this.secondStream$.subscribe` already — martin, Aug 16 '18 at 14:00
*I use switchMap*: no, not in the code you posted. Post the relevant code. — JB Nizet, Aug 16 '18 at 14:01

score 3 · Accepted Answer · answered Aug 16 '18 at 14:38

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.

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

1 Answers1