const {of, merge} = rxjs;

merge(of(1, 2, 3), of(4, 5, 6)).subscribe((v) =>
  document.body.insertAdjacentHTML('beforeend', `<div>${v}</div>`)
);

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/rxjs/7.8.1/rxjs.umd.min.js