Counter.scala

package scalm.counter

import org.scalajs.dom.document
import scalm.Html._
import scalm.{Html, Scalm}

object Counter {

  type Model = Int

  def start(): Unit = Scalm.start(document.body)(init, update, view)

  def init: Model = 0

  def update(msg: Msg, model: Model): Model =
    msg match {
      case Increment => model + 1
      case Decrement => model - 1
    }

  def view(model: Model): Html[Msg] =
    div()(
      button(onClick(Decrement))(text("-")),
      div()(text(model.toString)),
      button(onClick(Increment))(text("+"))
    )

  sealed trait Msg

  case object Increment extends Msg

  case object Decrement extends Msg

}

object TestCounter extends App {
  Counter.start()
}