Maybe I misunderstood your comment, but Deno is not a possible successor of Typescript, it is a possible successor to Node. Deno uses Typescript by default, by the way.

And Typescript may be slightly tricky to pick it for the first time when it comes to implement on existing codebases, but remember that it is a superset of JS, so valid JS is largely valid TS.

For argument validation, TS or Flow are the best tools. JSDoc, on the other hand, is a documentation standard, not exactly created for this purpose.