Example of basic HMR with Scala.js & Laminar

HMR.scala

object Main {
  val css: Css.type = Css

  println(s"PRODUCTION MODE: ${scala.scalajs.LinkingInfo.productionMode}")

  def main(args: Array[String]): Unit =
    waitForLoad {
      val appContainer = dom.document.querySelector("#app")
      appContainer.innerHTML = ""
      unmount()
      println("RENDER")
      val rootNode = render(appContainer, Frontend.view)
      storeUnmount(rootNode)
    }

  def waitForLoad(f: => Any): Unit =
    if (dom.window.asInstanceOf[js.Dynamic].documentLoaded == null)
      documentEvents.onDomContentLoaded.foreach { _ =>
        dom.window.asInstanceOf[js.Dynamic].documentLoaded = true
        f
      }(unsafeWindowOwner)
    else
      f

  def unmount(): Unit =
    if (scala.scalajs.LinkingInfo.developmentMode) {
      Option(dom.window.asInstanceOf[js.Dynamic].__laminar_root_unmount)
        .collect {
          case x if !js.isUndefined(x) =>
            println("UNMOUNT")
            x.asInstanceOf[js.Function0[Unit]]
        }
        .foreach { _.apply() }
    }

  def storeUnmount(rootNode: RootNode): Unit = {
    val unmountFunction: js.Function0[Any] = () => {
      rootNode.unmount()
    }

    println("STORE UNMOUNT")

    dom.window.asInstanceOf[js.Dynamic].__laminar_root_unmount = unmountFunction
  }

  if (`import`.meta.hot != null) {
    println("HOT RELOADING ENABLED")
    `import`.meta.hot.accept { (_: Any) => }
  }
}