There is a third backend, Scala.js https://www.scala-js.org

Based on the same principle as Scala Native, this one outputs javascript.

I've written a couple of projects where both the backend and front end is written in Scala, using one project, with different sub-projects for frontend/backend.

Scala.js will probably not convert Javascript developers en masse, but its very handy for Scala developers that prefer to write Scala to Javascript.