import { range } from "rxjs/observable/range";
import { map, filter, scan } from "rxjs/operators";

const source$ = range(0, 10);

source$
  .pipe(
    filter((x) => x % 2 === 0),
    map((x) => x + x),
    scan((acc, x) => acc + x, 0),
  )
  .subscribe((x) => console.log(x));