direct translation of virtual-dom example into scalajs, does not use functional idioms at all :-)

virtual-dom.scala

package tutorial.webapp

import language._
import scala.scalajs.js
import scala.scalajs.js.JSApp
import scala.scalajs.js.annotation.JSName
import org.scalajs.dom
import org.scalajs.jquery.jQuery
import dom.document
import scala.scalajs.js.timers._
import concurrent.duration._

trait VNode extends js.Object {
  def tagName: String = js.native
  def key: js.UndefOr[String] = js.native
  def namespace: js.UndefOr[String] = js.native
  def count: Int = js.native
  def hasWidgets: Boolean = js.native
  def hasThunks: Boolean = js.native
  def hooks: js.UndefOr[js.Dictionary[js.Any]] = js.native
  def children: js.Array[VNode] = js.native
  def properties: js.Dictionary[js.Any] = js.native
}

trait Patch extends js.Object

@JSName("virtualDom")
object VirtualDom extends js.Object {

  def create(node: VNode, opts: js.UndefOr[js.Object] = js.undefined): dom.raw.HTMLElement = js.native

  def diff(lhs: VNode, rhs: VNode): Patch = js.native

  def h(tagName: String, properties: js.UndefOr[js.Dictionary[js.Any]] = js.undefined,
    children: js.UndefOr[js.Array[js.Any]] = js.undefined): VNode = js.native

  def patch(rootNode: dom.raw.Node, patches: Patch): dom.raw.HTMLElement = js.native
}

object TutorialApp extends JSApp {

  import VirtualDom._

  def render(count: Int) = {
    h("div",
      properties = js.Dictionary[js.Any](("style", js.Dictionary[js.Any](
        ("textAlign", "center"),
        ("lineHeight", (100 + count).toString + "px"),
        ("border", "1px solid red"),
        ("width", (100 + count).toString + "px"),
        ("height", (100 + count).toString + "px")))),
      children = js.Array[js.Any](count.toString))
  }

  def main(): Unit = {

    var count = 0
    var tree = render(count)
    var rootNode = create(tree)
    document.body.appendChild(rootNode)

    val cancel = setInterval(1000) {
      count += 1
      val newTree = render(count)
      var patches = diff(tree, newTree)
      rootNode = patch(rootNode, patches)
      tree = newTree
    }
    setTimeout(10 seconds)(clearInterval(cancel))
  }

}