Typescript is JavaScript at runtime. It’s not a separate language, just like Python with type annotations (TypePython?) is just Python at runtime. Both are just type annotations that get stripped away before anything tries to run the code. That’s the genius of the idea and why it’s so easily adopted.
It is quite literally a separate language. Python's type hints are a part of the Python specification and all valid Python type hints will run in any compliant Python runtime. Typescript is not, in any way, valid JavaScript. The moment you add any type syntax, you can no longer run the code in Node or Browsers without enabling a special preprocess step.
