finalize.js

import { of, from } from 'rxjs';
import { switchMap, finalize, map } from 'rxjs/operators';

//emit (1,2,3,4,5)
const source = from([1, 2, 3, 4, 5]);
//add 10 to each value
const example = source.pipe(
  map(val => of(val).pipe( finalize(x=>console.log('final ' + val)))),
  switchMap(val=>val)
  );
//output: 11,12,13,14,15
const subscribe = example.subscribe(val => console.log(val));