Also, in that same startup, the same person writing the HTML, CSS, and JS is very likely also writing the server communication and building the production infrastructure, making the entire "front-end" distinction rather moot. Honestly, even in larger companies, the front-end/back-end specialization makes little sense to me. If you can write a good front-end javascript application, it's very likely you can write a good back-end in pretty much any stack.