You can do some truly silly things with sufficiently ridiculous uses of typescript. I built a typecheck-time spell checker[0] in it such that:

  import { ValidWords } from "./spellcheck";
  
  // Typechecks cleanly:
  const result: ValidWords<"the quick brown fox."> = "valid";
  
  // Throws a type error
  const result: ValidWords<"the qxick brown fox."> = "valid";

[0] https://github.com/kkuchta/TSpell

Your GitHub account is a rabbit hole of crazy interesting "monstrosities" like this. I love them! My favorite ones, apart from this typechecker, are css-only-chat[1] and tabdb[2]

1: https://github.com/kkuchta/css-only-chat 2: https://github.com/kkuchta/tabdb