I'm going to say something unpopular: it is possible to build and deploy real applications with just plain JavaScript and HTML. Not even Svelte and TypeScript.

I'm going to say something unpopular: it is possible to build and deploy real applications with just plain JavaScript and HTML. Not even Svelte and TypeScript. Just Javascript. I don't even use a CSS framework. Yeah you are allowed to do that if you are a hobbyist, or if you are like me and a solo developer of a product. We are allowed because no one can stop us. Component frameworks are useful though, and it is likely that if you bring in another developer to your project at a later date they will want to do it over in React or whatever flavor-of-the-month they like. In my opinion, if this happens it's okay, because by that time there will be new frameworks and web languages that are popular (e.g., suddenly next year all the cool kids build websites in Ocaml, Dream 3.0 and web assembly) and the old framework you used won't even necessary be relevant anymore. Also no one really wants to pick up another person's large codebase anyway. They will be happy to do it over their own way.