TypeScript is support on the frontend for oldtimers like me who have used plain JS for far too long and refuse to accept the torture of unnecessarily untyped languages any longer.
Also as already mentioned by others there exist web APIs.
It seems to be Golang based from what I can tell? And I'm guessing it either exposes a HTTP or WebSocket API, both which are usable from any language.
This is correct. It's golang and it exposes a plentiful API.