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))

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));

fn1(
  fn2(),
  fn3()
)