Integrating JavaScript components

Although Scala.js provides a superb environment for developing web clients, sometimes it makes sense to utilize the hard work of thousands of JavaScript developers fumbling in the shadows :)

Bootstrap CSS components

Bootstrap is a popular HTML/CSS/JS framework by Twitter for developing responsive applications. It comes with a lot of styled HTML/CSS components that are easy to use and integrate into your application. Many parts of Bootstrap actually don't even use JavaScript, all the magic happens in CSS.

This tutorial wraps a couple of simple Bootstrap components (button and panel) into React components. Bootstrap uses contextual styles in many components to convey additional meaning. These can be easily represented by a Scala enumeration.

object CommonStyle extends Enumeration {
  val default, primary, success, info, warning, danger = Value

To define an interactive button, it has to know what to do when it's clicked. In this example we simply pass a function to the properties alongside the contextual style. Note that the actual button contents don't need to be provided in the properties as it's more convenient to define it through child component(s).

object Button {

  case class Props(onClick: Callback, style: CommonStyle.Value = CommonStyle.default, addStyles: Seq[StyleA] = Seq())

  val component = ReactComponentB[Props]("Button")
    .renderPC((_, props, children) =>
      <.button(bss.buttonOpt(, props.addStyles, ^.tpe := "button", ^.onClick --> props.onClick, children)

  def apply(props: Props, children: ReactNode*) = component(props, children: _*)
  def apply() = component

This time the render method gets two parameters: The properties and the children given to this component. It simply renders a normal button using Bootstrap CSS and binds onClick to the handler we defined in the properties. Finally the children are rendered within the button tag.

Defining a Bootstrap Panel is about as simple.

object Panel {
  case class Props(heading: String, style: CommonStyle.Value = CommonStyle.default)

  val component = ReactComponentB[Props]("Panel")
    .renderPC((_, p, c) =>
        <.div(bss.panelHeading, p.heading),
        <.div(bss.panelBody, c)

  def apply(props: Props, children: ReactNode*) = component(props, children: _*)
  def apply() = component

The panel provides no interactivity but this time we define a separate heading in addition to using the children property.


Custom fonts are a great way to generate scalable icons that look good on all displays. In the tutorial we use Font Awesome icons and a simple wrapper that generates appropriate HTML tags to display the icon.

object Icon {
  type Icon = ReactTag
  def apply(name: String): Icon = <.i(^.className := s"fa fa-$name")

  def adjust = apply("adjust")
  def adn = apply("adn")
  def youtubePlay = apply("youtube-play")
  def youtubeSquare = apply("youtube-square")

JavaScript chart component

If you'd want a nice charting component in your web UI you could go ahead and write a lot of SVG-generating code, but why bother when there are so many components available for your benefit. Scala.js provides many ways to use JavaScript from your own Scala code and some of them are more type-safe than others. A good way is to define a facade for the 3rd party JS module and for any data structures it may expose. This way you can be sure to use it in a type-safe manner.

In the tutorial we are using Chart.js but the same principles apply to practically all JS components out there.

The Chart.js draws the chart onto a HTML5 canvas and is instantiated by following JavaScript code

var ctx = document.getElementById("myChart").getContext("2d");
var myNewChart = new Chart(ctx).Line(data);

To do the same in Scala.js we define a simple facade as follows

class JSChart(ctx: js.Dynamic) extends js.Object {
  def Line(data: ChartData): js.Dynamic = js.native
  def Bar(data: ChartData): js.Dynamic = js.native

Note that this defines only couple of charts available in the Chart.js component, but it's trivial to add more if you need them. We are also skipping the options parameter for charts to keep things simple.

To actually instantiate the chart, we need access to the canvas element and with React this is a bit problematic since it builds a virtual-DOM and updates the real DOM behind the scene. Therefore the canvas element does not exist at the time of render function call. To work around this problem we need to build the chart in the componentDidMount function, which is called after the real DOM has been updated. This function is called with a scope parameter that gives us access to the actual DOM node through getDOMNode(). The chart is built by creating a new instance of Chart and calling the appropriate chart function.

val Chart = ReactComponentB[ChartProps]("Chart")
  .render_P((P) => {
    <.canvas(^.width := P.width, ^.height := P.height)
  .componentDidMount(scope => Callback {
    // access context of the canvas
    val ctx = scope.getDOMNode().getContext("2d")
    // create the actual chart using the 3rd party component match {
      case LineChart => new JSChart(ctx).Line(
      case BarChart => new JSChart(ctx).Bar(
      case _ => throw new IllegalArgumentException

Chart.js input data is a JavaScript object like below

var data = {
    labels: ["January", "February", "March", "April", "May", "June", "July"],
    datasets: [
            label: "My First dataset",
            fillColor: "rgba(220,220,220,0.2)",
            strokeColor: "rgba(220,220,220,1)",
            data: [65, 59, 80, 81, 56, 55, 40]
            label: "My Second dataset",
            fillColor: "rgba(151,187,205,0.2)",
            strokeColor: "rgba(151,187,205,1)",
            data: [28, 48, 40, 19, 86, 27, 90]

To build the same in Scala.js we could directly use js.Dynamic.literal but that would be very unsafe and cumbersome. A better alternative is to define a builder function to create it and a facade to access it.

trait ChartData extends js.Object {
  def labels: js.Array[String] = js.native
  def datasets: js.Array[ChartDataset] = js.native

object ChartData {
  def apply(labels: Seq[String], datasets: Seq[ChartDataset]): ChartData = {
      labels = labels.toJSArray,
      datasets = datasets.toJSArray

In this case defining the ChartData trait is actually not necessary, since we don't really use it except to enforce type safety. But if you actually need to access a JavaScript object defined outside your application, this is the way to do it. Defining chart data is now as simple as

val cp = ChartProps("Test chart", Chart.BarChart, ChartData(Seq("A", "B", "C"), Seq(ChartDataset(Seq(1, 2, 3), "Data1"))))

If you need to build/access very complex JavaScript objects, consider an option builder approach like the one in Querki by jducoeur (for example JQueryUIDialog).

Bootstrap jQuery components

Bootstrap is not only a CSS library but also comes with JavaScript to add functionality to components like Dropdown and Modal. The Modal is an especially problematic system as it involves a hidden dialog box that is shown when the modal is activated and hidden afterwards. In a normal Bootstrap application you would define the dialog box HTML as part of your application and just keep it hidden. With React, however, it's easy (and recommended) to create the HTML for the modal just before it's displayed, so that your application can easily control the contents of the dialog box.

Before diving into the integration of the Bootstrap Modal, let's first examine how jQuery components can be integrated in general. We've provided a truly skeleton jQuery integration, just enough for the modal to work, so you'll want to use something more complete for most purposes. The jQuery integration is also briefly explained in Scala.js documentation so we won't go into the details too much. Basically you need to define a global jQuery variable, through which you can then access the jQuery functionality. This is done in the package.scala for the components package.

jQuery works by "calling" it with a selector or an element. In this tutorial we are always using a direct DOM element, so the facade only includes that option. For example to attach an event listener to an element, you would call

jQuery(scope.getDOMNode()).on("", null, null, scope.backend.hidden _)

jQuery has an extension mechanism where plugins can add new functions to the jQuery object. For example Bootstrap Modal adds a modal function. To define such an extension in Scala.js we create a trait for it and an implicit conversion (just a type cast, really) for it.

trait BootstrapJQuery extends JQuery {
  def modal(action: String): BootstrapJQuery = js.native
  def modal(options: js.Any): BootstrapJQuery = js.native

implicit def jq2bootstrap(jq: JQuery): BootstrapJQuery = jq.asInstanceOf[BootstrapJQuery]

Now whenever we want to call jQuery(e).modal() the compiler will automatically cast the JQuery type into BootstrapJQuery.

Armed with the jQuery integration we can now tackle the Modal itself. One of the problems the Modal poses is that it's dynamically shown and hidden by the Bootstrap code and we need to somehow control that. In this tutorial we've chosen a design where the modal doesn't even exist before it's needed and it's shown right after it has been created. This leaves only the hiding part for us to handle.

In the Backend of the Modal we define a hide() function to do just that.

class Backend(t: BackendScope[Props, Unit]) {
  def hide = Callback {
    // instruct Bootstrap to hide the modal

However, because the dialog box itself contains controls that need to actually close the dialog, we need to expose this functionality to the parent component via properties.

// header and footer are functions, so that they can get access to the 
// hide() function for their buttons
case class Props(header: Callback => ReactNode, footer: Callback => ReactNode, 
                 closed: Callback, backdrop: Boolean = true,
                 keyboard: Boolean = true)

Additionally, the Bootstrap modals are faded in and out, so the parent cannot go ahead and remove the modal HTML from DOM right away, but it needs to wait for the fade-out to complete. This is accomplished by listening to an event and calling the parent's closed function afterwards.

// jQuery event handler to be fired when the modal has been hidden
def hidden(e: JQueryEventObject): js.Any = {
  // inform the owner of the component that the modal was closed/hidden
// register event listener to be notified when the modal is closed
jQuery(scope.getDOMNode()).on("", null, null, scope.backend.hidden _)

To show the dialog box after it has been created, we again call modal() via jQuery in componentDidMount.

.componentDidMount(scope => Callback {
  val P = scope.props
  // instruct Bootstrap to show the modal
  jQuery(scope.getDOMNode()).modal(js.Dynamic.literal("backdrop" -> P.backdrop, "keyboard" -> P.keyboard, "show" -> true))

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