Deliver application as single HTML/JS file?

You can absolutely deliver an app this way. I code up little games for my kids in this way: https://letter-press.netlify.app/ If the intention is to just share the file around and have people open it locally, then the concerns stated by others about caching and CDN are non-issues. You will be extremely limited in what you can do in that environment. Lots of browser features don't work without a server running, and you won't have a backend.

The question I have is why do you have to distribute it as a single file?

If that were three files (bundle.js, bundle.css and index.html), it would be called “bundle without splitting”. Keywords: webpack, parcel, vite. Idk if these {css,js} files can be directly pasted into index.html’s link/script tags, but you can try with a simple example.

Added: please note that browsers tend to not cache index.html by default, so your single-file site will be re-downloaded on every access. You can it in , but then you’ll have a problem with updates, because all browsers out there will ignore the origin and use the cached version until it expires.

It doesn’t have a particular name. It’s not a good practice per se and probably that’s why it doesn’t have (as far asI know) a concrete denomination.

It is usually better to separate CSS and JS into files to get the benefits of the browser’s cache or the CDN. But of course you have your particular constraints.