[Tadpole9181]

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.

[hansifer]

Do you think JSX is a separate language?

[Tadpole9181]

Yes, JSX is a superset of JS and will not work in any tooling that is not explicitly JSX compatible. JS grammars will not parse it, it's not standard.