If no JavaScript then what enables interactivity?

Thanks for the question! I should have said almost no JavaScript:

There is a minimal amount of JavaScript just to download and run pyodide and then it is only Python: see example at

https://imgui-bundle.pages.dev/playground/?demo=p_35_minimal...

Very very impressive! So many use cases for this. Thanks again

Web assembly? This started out as a bowdlerised form of JavaScript (asm.js) but evolved to become is own thing.

You still need JavaScript to instantiate WebAssembly and let it interact with the page, which is why your sibling comment admits there's still a bit of JS.