import { zip } from 'rxjs/observable/zip';
import { interval } from 'rxjs/observable/interval';
import { from } from 'rxjs/observable/from';

import { delay } from 'rxjs/operators';

// Delay per-item. Also automatically completes once `from` completes
zip(
  from([1, 2, 3]),
  interval(1000),
).subscribe(([val]) => console.log(val));

// Delay only once
from([4, 5, 6]).pipe(delay(1000)).subscribe(console.log);