Hi, Alexander and everyone!
I've done a simple stupid IDE (CodeMirror based) with embedded RapydScript compiler + RapydML-like parser (mostly for writing Vue templates).
It emulates file system and utilizes localStorage to persist it (thanks to JSZip it is possible to store up to 20...25MB in 5MB - localStorage limit).
It is serverless and could be running locally as regular html.
It's also possible to download whole FS as zip or as single json-file (latter could be uploaded back!). Thus, you can compile pyj files (with imports support ) in the browser,
but the main feature is .vuepy files (that are similar to vue single component file) which could be imported as regular .pyj files in other .vuepy/.pyj files!
Html-playing from IDE FS including css and js is also supported (just add the attribute data-dynamic = 'true' to the script or css-link).
I did it time-to-time following frankenstein-pattern (source is horrible and must be refactored), so here is just a demo: