CompEventModel.scala

class Test {
  case class Item(
    name: String
  )

  case class Model(
    items: Vector[Item],
    selected: Item
  )

  def initial = {
    val fst = Item("a")
    Model(
      Vector(fst, Item("b"), Item("c")),
      fst
    )
  }

  sealed trait Event
  case object Noop extends Event
  case class Select(item: Item) extends Event

  def render(out: Handler[Event], in: Observable[Model]) = {
    div(
      in.map(state => state.items.map( item =>
        div(click(Select(item)) --> out, (
          if (state.selected == item)
            Some(cls := "active")
          else
            None
        ): Option[VDomModifier])(
          item.name
        )
      ))
    )
  }

  def handle: (Model, Event) => Model = {
    case (s, Select(item)) => s.copy(selected = item)
    case (s, Noop) => s
  }

  def view: VNode = for {
    handler <- Handler.create[Event]
    node    <- render(handler, handler.startWith(Seq(Noop)).scan(initial)(handle))
  } yield node
}

OutWatch.renderInto("#test", main()).unsafeRunSync()