> I wish there were an offline environment like that built into firefox. You can bring up a javascript console, but it's not really a friendly development environment. And something like visual studio code is capable but large and complicated.
That seems like a day project in electron. At least to MVP. Use CodeMirror or Monaco. As long as you pass the right options you can run the user's code in an iframe in a separate process. That way you can kill it even if it has an infinite loop.
I use BBEdit whenever I do web stuff (caveat: not a pro web dev) — if someone wanted to learn HTML/JS from scratch, I'd suggest a plain text editor like that.
Krita has: https://scripting.krita.org/lessons/introduction
while for Inkscape there is: https://inkscape.org/~pakin/%E2%98%85simple-inkscape-scripti...
Webmaker[1] isn't built in, but it does offer an offline code playground
There seem to be many online environments where you can type your {html, css, javascript} code and run it. For example, MDN has one at
https://developer.mozilla.org/en-US/play
(Unfortunately it has advertisements... which I suppose is incentive to learn how to use custom stylesheets.)
I wish there were an offline environment like that built into firefox. You can bring up a javascript console, but it's not easy to just type in code and run it. And something like visual studio code is capable but also large and complicated.