RxJS - How to incrementally increase the delay time without using interval?

Question

I want to incrementally increase the delay for this:

const source = from(839283, 1123123, 63527, 4412454); // note: this is random
const spread = source.pipe(concatMap(value => of(value).pipe(delay(1000)))); // how to incrementally increase the delay where the first item emits in a second, the second item emits in three seconds, the third item emits in five seconds, and the last item emits in seven seconds.
spread.subscribe(value => console.log(value));

I'm aware of using interval to incrementally increase the delay time as below. But I also need to consume this source const source = from(839283, 1123123, 63527, 4412454);

const source = interval(1000); // But I also need to use have this from(839283, 1123123, 63527, 4412454)
const spread = source.pipe(concatMap(value => of(value).pipe(delay(value * 200))));
spread.subscribe(value => console.log(value

How to incrementally increase the delay time when starting with const source = from(839283, 1123123, 63527, 4412454); ?

Answer 1

You can use the index of the emitted value and calculate the delay based on that.

concatMap((value, index) => {
  return of(value).pipe(delay((index > 2 ? 7 : index) * 1000));
})

Here is a stackblitz for a complete example with your snippet: https://stackblitz.com/edit/rxjs-jjmlta?devtoolsheight=60