first-value-from-will-not-wait-for-complete.ts

import { firstValueFrom, Observable, Subject } from 'rxjs';

async function demo<T>(observable: Observable<T>): Promise<void> {
  const result = await firstValueFrom(observable);

  console.log(result);
}

const subject = new Subject();
const obs = subject.asObservable();

demo(obs);
subject.next(1);
subject.next(2);
subject.next(3);


/* Observable is not completed yet, and will proceed to emit values */
obs.subscribe(console.log); 
subject.next(5);