[smt88]

You've been able to debug TypeScript (and anything else that transpiles to JS) natively in the browser for years using sourcemaps. That includes Dart, C#/F#, Go (as far as I know), and Python.

For the languages that target wasm instead, there are different debugging stories. Kotlin's is very good, Rust's is pretty immature.

[int_19h]

Source maps are not sufficient to fully expose the semantics of the language being debugged to the debugger. You also need the expression evaluator (for stuff like Watch etc) to understand what it's debugging. And in cases where transpilation includes nontrivial mapping of data structures, you also need the ability to do that mapping in reverse to display the values.

Source maps work great for TS because it is just "JavaScript with types" at this point.