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.
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.
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.
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.