Earlier quoted context omitted.
Do it like they did in the good old days when JS was new and couldn't be relied upon to exist. Don't rely upon it to exist. Serve up well marked content, CSS that might format it nicely, and JavaScript that allows some types of per-validation to happen client side but only as a means of making a page nicer. The server side should STILL perform all data validation, normalization, and verification (assume someone will…
No, Twitch specifically. It's an interactive chat and live video streaming application that happens to be built out of web tech. If you don't have AJAX, you could maybe-kinda-sorta kludge it together out of forms and video elements, but it'd degrade hard , and need to be built completely different from the normally-interactive version.
Twitch could be done with a native app... the phone versions SHOULD be done with such if they aren't.