Still a nifty new tool though. I wish JS would just allow type declarations at this point. It doesn't need to enforce them, just allow them like Python does. That would be amazing.
But this is just an on-the-fly transpile(natively supported). It would be much better if JavaScript would go the Python route. For that they would have to extend the EcmaScript spec (to be safe) I guess.
Just using JSDoc is imho not a good alternative. The big benefit of TypeScript is that your compiler checks this all for you. I've seen to much incomplete or wrong JSDoc in my life.. also a nightmare to maintain.
Open a js file with ts comments, and it silently converts to ts editing. Save the file and it converts ts back to js with comments before actually writing.