This is the curse of guest languages, after the initial adoption pain everyone wants idiomatic libraries and pretends the underlying platform doesn't exist.
Until they hit a roadblock caused by a leaky abstraction, that proves them otherwise.
Type script does a very good job not to hide the underlying platform. In it's essence it is just a development time linter and does not interfere with the JavaScript runtime at all (except enums).
And I think that's actually the reason why it won the competition against Googles Dart. They even used Microsofts TypeScript for Angular instead of their own language Dart.
Until they hit a roadblock caused by a leaky abstraction, that proves them otherwise.