I just thought: will it be possible and reasonable to update Exercism’s editor for TypeScript to something more easy-to-use, with highlights, completion editor like this one. Hope TS Playground provides integration point. Didn’t check it
Before we launched v3 I had extensive talks with @iHiD about this subject. It’s on the radar, but most likely not any time soon.
The next goal would be to get the interface up for all languages to provide LSP (Language Server Protocol) server or service which can provide both (structured) syntax highlighting and autocomplete, instead of having a sorta-bespoke solution for one or a few languages.
Until then, if you were to do these offline, I highly recommend VSCode.