It's still written in Ur/Web. And the type-safety of Ur/Web is the reason I started writing it -- I couldn't imagine myself using untyped JavaScript.
Ur/Web is not very practical for reasons other than type safety: the lack of libraries and slow compilation when the project gets big. The language itself is good, though.
Nowadays, I would probably choose OCaml. It doesn't have Ur/Web's high-level features, but it's typed and compiles quckly.
Whoa, that's cool!
What do you think about Typescript? I mean it's unsound but - it sounds like an ok compromise
Didn't use TypeScript, so can't say much. I guess some types are better than no types, and it's easier to use for JavaScript developers.
Personally, I'd prefer a fully typed language.
https://github.com/urweb/urweb
http://www.impredicative.com/ur/
Needless to say it wasn't very practical. But there was one commercial site written in it https://github.com/bazqux/bazqux-urweb (the site still exists but not sure if it's still written in ur/web)