Comment by tjallingt

Some examples of "transpilers" targeting Javascript but writen in other languages:

https://github.com/google/closure-compiler

https://github.com/BuckleScript/bucklescript

https://github.com/fastpack/fastpack

Seems like on the average it does offer a boost in performance.

And there is some aditional work providing javascript parsers for rust (which you could build tools like babel on top of): https://github.com/dherman/esprit