The parent's point was that you don't need Javascript for that; some of the state (i.e., the state of the parent dropdown) could be stored in the URL, or in a f

The parent's point was that you don't need Javascript for that; some of the state (i.e., the state of the parent dropdown) could be stored in the URL, or in a form variable...which is how things were done in the days before Javascript. Yes, you would need multiple pages. But that is how most form-based SPAs work today anyway, and avoiding a page reload isn't always preferrable to just reloading if the SPA version requires heavy amounts of JS and the good-old-static version loads in the blink of an eye.