Scala LanguageScala.js


Scala.js is a port from Scala that compiles to JavaScript, which at the end will be running outside the JVM. It has benefits as strong typing, code optimization at compile time, full interoperability with JavaScript libraries.

console.log in Scala.js

println("Hello Scala.js") // In ES6: console.log("Hello Scala.js");

Fat arrow functions

val lastNames = => p.lastName)
// Or shorter:
val lastNames =

Simple Class

class Person(val firstName: String, val lastName: String) {
  def fullName(): String =
    s"$firstName $lastName"


val personMap = Map(
  10 -> new Person("Roger", "Moore"),
  20 -> new Person("James", "Bond")
val names = for {
  (key, person) <- personMap
  if key > 15
} yield s"$key = ${person.firstName}"

Manipulating DOM

import org.scalajs.dom
import dom.document

def appendP(target: dom.Node, text: String) = {
  val pNode = document.createElement("p")
  val textNode = document.createTextNode(text)

Using with SBT

Sbt dependency

libraryDependencies += "org.scala-js" %%% "scalajs-dom" % "0.9.1" // (Triple %%%)


sbt run

Running with continous compilation:

sbt ~run

Compile to a single JavaScript file:

sbt fastOptJS