90% of VS Code is typescript that already works fine in the browser. There's just a small layer of nodejs to interface with the local filesystem and run processes. Quite a few projects have existed that pull the core of VS code out into the browser and reimplement the small platform layer on their own:

- Eclipse Theia: https://github.com/eclipse-theia/theia

- Coder: https://github.com/cdr/code-server

I'm sure there are countless versions for mobile that are hasty Cordova-based versions of the VS Code core too.

VS Code is essentially a browser app based on Typescript(Javascript) and html. You can even open the chrome dev tools in VS Code (Help -> Toggle Dev Tools) and inspect the html and javascript of VS code. You can also go so far as to change the CSS and html of vs code in the dev tools. Try using the element picker (top left icon in the dev tools) to select an element in vs code, and you'll see that each line of code is a div and each token is a span that is syntax highlighted by CSS classes.

The desktop app runs on electron, which is Chrome under the covers, so I imagine it doesn't take a tremendous amount of work to just run it straight in the browser.

The world is starting to scare me. I think I'll go live under a rock and wait it out until the pendulum swings back and people stop thinking of the browser as their OS.

(Electron = Chromium minus tab bar and window borders)

I mean, it already basically does