Probably all the same selling points that Scala/JVM has over Java or Kotlin. The main one would be favoring a coding style with immutable data, only reaching fo

Probably all the same selling points that Scala/JVM has over Java or Kotlin. The main one would be favoring a coding style with immutable data, only reaching for mutability when necessary. If you like that style, Scala.js will help you write in that style. See also one of my other answers with some more comparisons.