I think this is an excellent suggestion (I'm OP / author), and one one can add just a dash to this for typechecking. Minimal setups are appreciated, especially when one has many small projects.

Glad I could help! Esbuild won't do the actual type-checking for you, but your editor will (hopefully also without configuration)

I'll put it this way: I've spent enough time with Webpack and Babel and TSC at this point that I can troubleshoot most issues without too much difficulty. But despite that I reach for esbuild every time I possibly can, because I just don't want to mess with all that stuff if I don't have to.

There's also js_of_ocaml if a good type system is desired.

I think that's out of scope for the OP's needs/wants. They like TypeScript for catching basic API mistakes, the only thing they don't want is configuration headaches. I didn't get the sense they would be interested in learning a new language for this use-case, especially since I'm going to guess Cloudflare doesn't publish OCaml types for their JavaScript API.

That's fair. Guess I just got excited about an opportunity to plug js_of_ocaml ;)

When we wrote opalang, the size of generated JS was problematic, despite serious efforts at minimizing it. Does js_of_ocaml do better?

I'm not familiar with opalang, but I haven't noticed size issues with js_of_ocaml (though I've only used it for personal projects). It works by compiling OCaml bytecode to JS. I think the main thing you'd need to be careful about in terms of code size is which libraries you end up relying on.

EDIT: There's also bucklescript, which goes from OCaml to JS (skips the bytecode), but I think it is more relaxed in terms of preserving OCaml behavior. i.e., it relies on how JS behaves for certain operations, instead of trying to preserve how natively compiled OCaml would behave.