Doesn't have to be, it's not very popular these days but we used to talked about progressive enhancement, the idea being you should prerender your thing in HTML

Doesn't have to be, it's not very popular these days but we used to talked about progressive enhancement, the idea being you should prerender your thing in HTML and spice it up with JS, this is also covered in the POC and is unfortunatly something that got lost over time in favor of "modern framework" and the new meta everything fad