It is the best of tools; it is the worst of tools. It is indispensable; it is unusable. It makes the impossible possible; it makes easy things hard. Nothing ever breaks; nothing ever works.
I like the sass, much less the typescript.
Yeah the way you need to maintain two codebases: one for types and one for actual logic is annoying.
Also nix is purely functional (which is necessary, for more information read the Nix Pills), Typescript is not, so unless it's only a purely functional subset or severely limits Nix (in the form of abstractions, after skimming over it, I think this is the case), it will run into issues...
But why typescript? Why not nickel or any other better suited functional lazy language with types?
Here's what author says.
With Typescript, you get the full power of programming — the ability to easily factor out variables, to connect and abstract functionality, to reuse code, to write tests. But you don't need to learn a new language. You don't need to find documentation (it's right there in your editor, if you have LSP set up). You don't need to try to make sense of a page of Nix traceback (type errors will show you where you went wrong much earlier and more precisely).
I personally agree with this. Learning a new language that is poorly documented is pretty difficult. (I still learn Nix though since I think it's fun)
If this state will persist, Nix will end up being like haskell with exclusive community, which leads fhe language itself to death.