You might be aware of it already, but I just wanted to mention that the Zod library could potentially solve some of your needs.

Yes, that and the openapi plugin is what i use right now. Before i used to load the ts compiler at runtime and tell it to parse my file and got the types from there. But it was a stupid overengineered brittle solution.

How would Typescript do that while transpiling to JS? It would need to add a whole lot of boilerplate code to the generated JS, slowing the execution down.

Does it not already do this? I don’t use TS if I have the choice due to all the runtime complexities, including the endless house-of-cards shimming it does to prop up all the features of TypeScript.

No, typescript has full type erasure and almost no type-directed emit. The shimming you're seeing is probably the result of tsc downleveling newer javascript features to older browsers: typescript itself has nothing to do with it.

https://www.typescriptlang.org/tsconfig#target

Try running tsc in ES2020 mode, the output will be surprisingly clean JavaScript. Older versions include a lot of hacks for dynamic module loading, etc.

Something like typeinfo<T> being inlined into an object describing my type. Totally opt-in, no need for every type to be tracked at runtime.

Why should types even exist at runtime? Everything should be validated at compile time and then the whole concept of types no longer needs to exist.

You are sometimes interacting with external data. Particularly in web land, you don't know for sure if the payload meets expectations until you check.

Plenty of solutions here such as code generation or Elm style combinators. I’m not convinced that Python style runtime meta programming is a particular robust solution since it is not (easily) checked statically.

Sure. But it would be nice not to need to describe the structure of your data twice if you need runtime validation. Since TS is such an ergonomic way of describing the structure of your types, runtime availablility is more attractive (to some) than relying on external libraries for that functionality.