For me, at least with TypeScript the single biggest advantage is the hinting you get from 3rd party packages/modules. This goes for building modules as well, you can use jsdoc directly, but it's even more cumbersome than TS imo.
It's kind of annoying that static type introspection has become the norm for language servers because live environments are so much better. With Ruby you have the REPL and there have been IDEs and tools that allow runtime reflection which is just so much better (think Lisp or Smalltalk). LSPs are nice for static languages but compared to live environments they're a step down...
