It's also worth noting that Scala / Scala.js includes lots of features that JS developers use a plethora of third party libraries for. For example JS has no im

It's also worth noting that Scala / Scala.js includes lots of features that JS developers use a plethora of third party libraries for. For example JS has no immutable collections built-in, so you'd need something like immutable.js (65KB) which is annoying to use because it's not integrated with other libraries or language features, whereas Scala libraries obviously work well with Scala collection types. Or take Scala's implicits vs React.js context. The latter is what you need to invent when your language has no concept of implicit parameters, and it's a poor, library-specific, substitute.