JScala supports ternary operator expressions.

gistfile1.scala

val ast = javascript {
  def main(args: Array[String]) {
    val language = if (args.length == 0) "EN" else args(0)
    val res = language match {
      case "EN" => "Hello!"
      case "FR" => "Salut!"
      case "IT" => "Ciao!"
      case _ => "Sorry, I can't greet you in " + language + " yet"
    }
    console.log(res)
  }
}
println(ast.asString)

gistfile2.js

{
  function main(args) {
    var language = (args.length == 0) ? "EN" : args[0];
    var res;
    switch (language) {
      case "EN":
        res = "Hello!";
        break;
      case "FR":
        res = "Salut!";
        break;
      case "IT":
        res = "Ciao!";
        break;
      default:
        res = ("Sorry, I can't greet you in " + language) + " yet";
        break;
    };
    console.log(res);
  };
}