In general I'd advise against using Scala.js for libraries. The Scala.js runtime is pretty heavy, and Scala's and TypeScript's type systems are different enough that it tends to be difficult to design an API that feels native in both.

Have you considered ScalaJS-React[0] or Outwatch[1] instead?

[0]: https://github.com/japgolly/scalajs-react

[1]: https://outwatch.github.io/?lang=scala