Syntax

import { interval, of } from 'rxjs';
import { map, take, concatMap } from 'rxjs/operators';

const randomString = () => Math.random().toString(36).slice(2);

const source$ = interval(200).pipe(
  take(100),
  concatMap((i) =>
    i % 10 === 0 ? of(`${randomString()}\n`) : of(randomString())
  )
);

source$.subscribe(console.log);

import { interval, of } from 'rxjs';
import { map, take, concatMap } from 'rxjs/operators';

const randomString = () => Math.random().toString(36).slice(2);

const source$ = interval(200).pipe(
  take(100),
  concatMap((i) =>
    i === 99
      ? of({ data: `${randomString()}\n` })
      : of({ data: randomString() })
  )
);

source$.subscribe(console.log);

• Nestjs @Sse : return result of a promise in rxjs observable - Stack Overflow