It took me time to work out where to start... Once you think it through you realise it is pretty easy and obvious. But (and this gives away my age a bit), I have not built a static webpage since school (over 10 years ago), and have become so accustomed to all the crazy shit that goes into web development today like Webpack, NPM, React, Angular etc etc that I had forgotten how to actually just serve a piece of HTML.
My dependence on all these frameworks and CLIs sent me on a quest to find out more about pure javascript, and I came across an incredible talk by a developer who created a pure javascript web app for music notation. I really wanted to link it here but cannot find it.