I agree TS is great. Not really multi threaded kills it for me though.
Node.js: https://nodejs.org/api/worker_threads.html
Browser: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers...
However, threads are very rarely needed. The common use case in other languages is I/O, and JS environments handle that with async I/O—a superior choice, IMO.
And the language and the VM has been, and will be for any foreseeable future, single-threaded.
Whatever it supports, Javascript-the-language has no concept of threads. And workers are basically external processes with a somewhat awkward event-based communication and certain limitations.
Whatever Deno uses internally to implement them has no bearing.