A web application with Play, ScalaJS, ReactJS - Part IV

In the recent articles within this series we have created a small Play application that provides a REST interface to manipulate a simple business object. We have also set up a toolchain consisting of services that are available online and therefor we have minimized the overhead of setting up any development infrastructure ourselves.

In this article we will finally kick off our web development. The overall goal for this article is to get a ReactJS component integrated into the application which displays the list of available seminars within a browser, so that we can extend that component in the next part to support all the operations of the REST service.

The source code behind this article is in the project’s github repository within the branch 03_InitialWebClient.

So far in this series:

Quick review of what’s required

The main theme of this article is to get everything in place, so that we can start developing in ScalaJS for the frontend and also use Bootstrap to style the content of the application. For bootstrap we want to use LESS to have the maximum flexibility in our stylesheets.

For the ScalaJS code we need to set another module and configure the ScalaJS compiler. The compiled result must end up within the javascript resources of the Play application.

Once we have the toolchain out of the way we will gear towards our first ReactJS component talking to the server side REST interface.

Configuring Bootstrap for the project

Let’s get started by getting bootstrap into the sources of our play application. As we want to use LESS we need to download the source code of bootstrap from the Bootstrap homepage.

Unzip the zip with the bootstrap sources and within the unzipped sources you will find a less subdirectory. Assuming $PRJ_HOME is the root directory of the project, we need to copy the less folder of bootstrap to $PRJ_HOME/server/app/assets/stylesheets/less/bootstrap.

Bootstrap also comes with a collection of Glyphicons in the dist/fonts directory of the downloaded bootstrap archive. If you plan to use those copy the folder dist/fonts to $PRJ_HOME/server/app/assets/stylesheets/fonts.

Your own LESS files would end up in $PRJ_HOME/server/app/assets/stylesheets/less. For convenience we will refer to this directory as $LESS_SRC. Following the suggestions from Extending Bootstrap, create a file _main.less in $LESS_SRC with the following content:

1 @import "bootstrap/bootstrap";   // Import the original bootstrap less files
2 @import "_variables";            // override any variables for bootstrap/variables
3 @import "custom-styles";         // any custom styles we want to apply

Just for fun and to see whether the stylesheets are pulled in correctly we define in _variables.less

@brand-primary:         #123f64;
@body-bg:               blue;

and finally in custom-styles.less

@brand-primary:         #123f64;
@body-bg:               blue;

The next step is to make the play application aware of the LESS files so that they are added to the application’s resources. Luckily Play supports the compilation of LESS file with the sbt-less plugin, so we add this to our list of plugins in project/plugins.sbt:

resolvers += "Typesafe repository" at "http://repo.typesafe.com/typesafe/releases/"

addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.7")

addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "0.8.0-RC2")

addSbtPlugin("com.typesafe.sbt" % "sbt-less" % "1.0.0")

addSbtPlugin("org.scoverage" % "sbt-scoverage" % "1.0.1")

addSbtPlugin("com.codacy" % "sbt-codacy-coverage" % "1.0.0")

By default the plugin looks for a file main.lesswithin $LESS_SRC, so we need to override that setting within our build file:

 * The settings for the server module
lazy val serverSettings = commonSettings ++ Seq(
  name := s"$appName-server",
  libraryDependencies ++= Dependencies.serverDeps,
  includeFilter in (Assets, LessKeys.less) := "__main.less"

As bootstrap also has javascript components, we add bootstrap as a dependency to the server module using webjars, so that the required javascript libraries can be pulled in to our html templates via the assets controller:

lazy val serverDeps = Seq(
  "com.newrelic.agent.java" % "newrelic-agent" % Versions.newRelic,
  "org.webjars" % "bootstrap" % Versions.bootstrap,
  "org.scalatestplus" %% "play" % Versions.scalaTestPlus % "test"

What remains is to change the html template so that it uses the defined styles:

<!DOCTYPE html>

      <title>Just Play Scala</title>
      <link rel="stylesheet" href="assets/stylesheets/less/__main.css" >
      <h1>Just Play Scala</h1>

      <button type="button" class="btn btn-default" aria-label="Left Align">
        <span class="glyphicon glyphicon-align-left" aria-hidden="true"></span>

      <script src="assets/lib/bootstrap/js/bootstrap.min.js"></script>
      <script src="assets/lib/jquery/jquery.min.js"></script>

As you can see, all the resources are now available via the assets controller, which is in general used to serve static content for the Play application. Now we have everything in place give it a go and start the server:

$ sbt
[info] Loading project definition from /Users/andreas/projects/play/castillo/project
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.typesafe.sbt:sbt-native-packager:0.7.4 -> 0.8.0-RC2
[warn] Run 'evicted' to see detailed eviction warnings
[info] Set current project to castillo (in build file:/Users/andreas/projects/play/castillo/)
> project server
[info] Set current project to castillo-server (in build file:/Users/andreas/projects/play/castillo/)
[castillo-server] $ run

--- (Running the application, auto-reloading is enabled) ---

[info] play - Listening for HTTP on /0:0:0:0:0:0:0:0:9000

(Server started, use Ctrl+D to stop and go back to the console...)

Now we can navigate to http://localhost:9000 and we should see the same content as before, but bootstrapped ;):

Just Play Scala with Style

Yes, it’s not nice, but it shows the point …

Hello ReactJS

Now that we have the LESS files and Bootstrap out of the way for now we can turn to getting ScalaJS and ReactJS support into the project. I tend to try and set up the tooling first and see if everything works before I turn to the actual programming task. This having said, let’s use one of the examples of the ReactJS tutorial and stick it on the entry page of our application - just to make sure that we can compile everything and assemble the application.

A Hello React Component

The React component I selected simply says hello to someone and counts the number of seconds elapsed since the page has been displayed. In React terms the component’s state is the number of seconds elapsed, while the person we are saying hello to is not. The latter is simply an initialization parameter, but doesn’t change after the component has been instantiated.

In other words: Only things that change over time make up the React components’ state.

The state of the first component is built from the previous state by increasing the number of elapsed seconds by 1 and we make sure that this happens every second. Finally we set up the component in the main method and we are done.

Note: I am not going into the details of ReactJS or ScalaJS here as we are only interested in setting up the build for now.

 1 package de.woq.castillo.client
 3 import japgolly.scalajs.react.{ComponentScopeM, ReactComponentB}
 4 import japgolly.scalajs.react.vdom.ReactVDom.all._
 5 import org.scalajs.dom
 6 import org.scalajs.dom.window
 7 import scala.scalajs.js
 8 import scala.scalajs.js.JSApp
10 object HelloReact extends JSApp{
12   case class State(secondsElapsed : Long)
14   class Backend {
15     var interval : js.UndefOr[Int] = js.undefined
16     def tick(scope : ComponentScopeM[_, State, _]) : js.Function =
17       () => scope.modState(s => State(s.secondsElapsed + 1))
18   }
20   val helloCastillo = ReactComponentB[String]("appMenu")
21     .initialState(State(0))
22     .backend(_ => new Backend)
23     .render((param,s,_) => div(
24     h2(s"Hello from React, $param !"),
25     h3(s"Time elapsed : ${s.secondsElapsed}s")
26   ))
27     .componentDidMount(scope =>
28     scope.backend.interval = window.setInterval(scope.backend.tick(scope), 1000))
29     .componentWillUnmount(_.backend.interval foreach window.clearInterval)
30     .build
32   def main(): Unit = helloCastillo("Andreas") render dom.document.getElementById("content")
34 }

The code for the component goes into a new module of our application client into the src/main/scala folder as it would for any other Scala module. Within the client module again we create a symbolic link shared -> ../shared, so that the client also takes the shared Scala sources into account.

Using the component with a Play view

Assuming the component above would be compiled into JavaScript and would be in the right place to be accessible from our entry page, we could just write the entry page like this:

 1 <!DOCTYPE html>
 3 <html>
 4   <head>
 5     <title>Just Play Scala</title>
 6     <link rel="stylesheet" href="assets/stylesheets/less/__main.css" >
 7   </head>
 8   <body>
 9     <div id="content"></div>
11     <script src="assets/lib/jquery/jquery.min.js"></script>
12     <script src="assets/lib/bootstrap/js/bootstrap.min.js"></script>
13     <script src="assets/lib/react/react.min.js"></script>
14     <script src="assets/javascripts/castillo-client-fastopt.js"></script>
16     <script type="text/javascript">
17       de.woq.castillo.client.HelloReact().main()
18     </script>
19   </body>
20 </html>

Apart from the scripts we have imported for bootstrap support we add the react javascript library to the mix. Finally, our own client library has the ReactJS component compiled into javascript and we can call the main method of the component the create an instance of it and bind it to the div container named content.

Adjust the build definition

In order to make that work, some adjustments to project/CastilloBuild.scala are required, so let’s look at them one by one:

Add the ScalaJS plugin to the project

To use ScalaJS we need to use the sbt plugin that allows to compile Scala to javascript, so we add this to project/plugins.sbt:

addSbtPlugin("org.scala-lang.modules.scalajs" % "scalajs-sbt-plugin" % "0.5.6")

Define the client module

The client module should look fairly familiar. We simply define a new project that lives in the client directory and pull in the clientSettings that we defined in it’s own variable for readability reasons. Also we need to pull in the scalaJSSettings that are pre-defined within the ScalaJS plugin. By using those settings the compiler for that module is set to the ScalaJS compiler, so that the compiled artifacts will be javascript.

 * Define the client project as a ScalaJS application.
lazy val client =


 * The settings for the client module (ScalaJS)
lazy val clientSettings = commonSettings ++ Seq(
  name := s"$appName-client",
  libraryDependencies ++= Dependencies.clientDeps.value
) ++ sharedDirSettings

We also need to make a small adjustment to the definition of the server module as it now need to aggregate the client module:

 * Define the server project as a Play application.
lazy val server =
  .enablePlugins(PlayScala) aggregate client

Define the client dependencies

Now let’s have a look at the client dependencies. The client dependencies are actually dependencies to Scala libraries that have been compiled for javascript already. When we compile our own Scala code to javascript, the result will contain the javascript code of these dependencies. In other words, these dependencies have nothing to do with the javascript libraries that we need to pull into our HTML.

Let’s use the HelloReact example to digest that a bit more. The client dependencies of the client are defined as

lazy val clientDeps = Def.setting(Seq(
  "com.github.japgolly.scalajs-react" %%% "core" % "0.6.1",
  "com.github.japgolly.scalajs-react" %%% "test" % "0.6.1" % "test",
  "com.github.japgolly.scalajs-react" %%% "ext-scalaz71" % "0.6.1",
  "org.scala-lang.modules.scalajs" %%% "scalajs-dom" % Versions.scalajsDom,
  "com.scalatags" %%% "scalatags" % "0.4.0",
  "org.scala-lang.modules.scalajs" %%% "scalajs-jquery" % "0.6",
  "org.scala-lang.modules.scalajs" %% "scalajs-jasmine-test-framework" % scalaJSVersion % "test"

Consider the dependency to scalajs-react/core. This brings the Scala wrapper for ReactJS into the project and by using that wrapper the compiled of our project will also include the javascript code for the wrapper. No special import is required within the HTML page. However, the wrapper of course uses the ReactJS javascript library under the covers and this is not pulled into the compiled javascript of the project. In order to use the code that relies on the wrapper, we have added react.min.js to the imported javascripts of our HTML page.

To have ReactJS available in our assets, we have added the webjars dependency to the server dependencies:

lazy val serverDeps = Def.setting(Seq(
  "com.newrelic.agent.java" % "newrelic-agent" % Versions.newRelic,
  "org.webjars" % "bootstrap" % Versions.bootstrap,
  "org.webjars" % "react" % Versions.react,
  "org.scalatestplus" %% "play" % Versions.scalaTestPlus % "test"

Adjust the server project

With the changes so far we have defined a client module where the Scala source is compiled into javascript. Now we need to adjust the server module to achieve:

  • Whenever the server module is compiled we also want to compile the Scala code in the client module, so that the project’s javascript library is updated.
  • The javascript library must be present in the server’s public/javascripts directory, so we will change the target directory for the compiler to achieve this.
  • We want to provide source maps for easier debugging, so we copy those as well to the server’s public/javascripts directory.

This gives us the following updated definition of the server project:

lazy val serverSettings = commonSettings ++ Seq(
 name := s"$appName-server",
 scalajsOutputDir := (classDirectory in Compile).value / "public" / "javascripts",
 compile in Compile <<= (compile in Compile) dependsOn (fastOptJS in (client, Compile)) dependsOn copySourceMapsTask,
 dist <<= dist dependsOn (fullOptJS in (client, Compile)),
 stage <<= stage dependsOn (fullOptJS in (client, Compile)),
 libraryDependencies ++= Dependencies.serverDeps.value,
 includeFilter in (Assets, LessKeys.less) := "__main.less"
) ++ (
 // ask scalajs project to put its outputs in scalajsOutputDir
 Seq(packageExternalDepsJS, packageInternalDepsJS, packageExportedProductsJS, packageLauncher, fastOptJS, fullOptJS) map { packageJSKey =>
   crossTarget in (client, Compile, packageJSKey) := scalajsOutputDir.value
) ++ sharedDirSettings

The only additional thing here is, that we use different optimizations for the final javascript when we build the development version or the final version. The latter uses Google closure compiler underneath to remove any unused javascript from the compiled library, so that it is smaller and can load faster.

A rudimentary component displaying the list of available seminars

So, we got a web page going with ScalaJS and React, now let’s turn it into displaying a list of seminars. This is quite simple going from the initial ReactJS example by defining the state of the component in terms of our portfolio rather than elapsed seconds:

case class State(portfolio : List[Seminar])

This is possible because we have modified the build definition earlier to include the shared Scala sources within the Scala JS client. Now we can get rid of the dynamic portion of the backend code as we don’t count the number of elapsed seconds anymore:

class Backend

Within the component we provide a very simple method to render the list of available seminars and we initialize the list of available seminars after the component has mounted:

val helloCastillo = ReactComponentB[String]("appMenu")
  .backend(_ => new Backend)
  .render((param,s,_) => {
    def createSeminar(seminar: Seminar) = div(
      p(s"Trainer ${seminar.details.trainer} -- ${seminar.details.duration} days")

      h2(s"Our course portfolio"),
      div(s.portfolio map createSeminar)
  .componentDidMount(scope =>
      Seminar(1, SeminarDetails(
        title = "My cool Seminar",
        description = "React Seminar",
        trainer = "andreas@wayofquality.de",
        duration = 5

After these changes we have a react component that will initialize itself with a static list of seminars upon initialization:

A preconfigured list of seminars

Communicating with the server

The final step for today’s article is to get the list of available seminars from the server. This should be straight forward by replacing the code to initialize the list with a call to our REST interface and de-serialising the result into a list of seminars.

Fortunately, Li Haoyi provides a ready-to-go library for simple JSON de(serialisation) within ScalaJS - upickle, so that the final component looks like this:

object HelloReact extends JSApp{

  case class State(portfolio : Seq[Seminar])

  class Backend

  val helloCastillo = ReactComponentB[Unit]("HelloCastillo")
    .backend(_ => new Backend)
    .render((_,s,_) => {
      def createSeminar(seminar: Seminar) = div(
        p(s"Trainer ${seminar.details.trainer} -- ${seminar.details.duration} days")
        h2(s"Our course portfolio"),
        div(s.portfolio map createSeminar)
    .componentDidMount(scope => {
      val url = "/portfolio"
      Ajax.get(url).foreach { xhr =>
        val seminars = upickle.read[Seq[Seminar]](xhr.responseText)

  def main(): Unit = React.render(helloCastillo(), dom.document.getElementById("content"))


Note: We have started with Long as the type for the primary identifier of our seminars. It seems, that values of type Long are (de)serialized as Strings within upickle but as JSON numbers on the server side. To get this initial example going, we have decided to change the seminar type to use Strings as the primary identifier, so that both sides are (de)serialized in the same way.

The complete code for the example is available on github.


Now we have a Play application exposing a CRUD like REST service for seminars and a rudimentary React Component using that service to retrieve and display the list of available seminars. In the next article we will flesh out that component, so that it supports the other operations of the service as well. That will also allow us to dive a bit deeper into the ReactJS world.

We have also set up the first cut of the LESS compilation, so that we can work with our own copy of Bootstrap while we develop the application.

Further ahead we will then introduce Authentication and Authorization, so that access to data modification operations can be restricted. Once we reached that point we will turn to fleshing out the UI design of the application and see how ScalaJS can help us keeping things nice and tidy.

As usual, feel free to contact me with questions, comments or corrections in case I missed something.