Comment by q-rews

You read that out of context. We’re talking about apps, web apps, SPAs, and specifically situations that bring you to mix HTML and CSS into a JavaScript module.

That situation most likely requires HTML (DOM) generation in the browser, which can only happen in JavaScript.

So, I reiterate, the HTML is generated by JS in these interactive modules.

You could generate the HTML on the server and then use jQuery to toggle elements… or just create full-JS components that take care of everything, giving some input data, instead of separating the HTML from the JS.