ReactJS Tutorial with Play, Scala and WebJars.

This tutorial goes in combination with the Facebook introduction tutorial on React.js. The code of this project is available here on GitHub.

I do mostly backend & mobile development, but am very interested in the direction the web is going. I decided to follow the basic React tutorial from Facebook and implement it using Play Framework and, most crucially, WebJars. It took me quite a few hours to get the whole thing working together, so I’m now writing about hoping to help someone else.

WebJars are client-side libraries packaged into JAR files, ready to be included in any JVM based project. They are available on Maven and therefore accessible via most build tools such as Maven, Gradle or SBT. The Play Framework offers support for WebJars, but getting it all to work wasn’t as smooth. Let’s go!

First of all, setup a new basic Play application using Activator:

activator new <your-app-name>

Choose play-scala as starting point and fire up your development tools. I personally favor IntelliJ with the Scala plugin, which allows you to import the project from an external SBT module.

The first thing you want to do with a view on using WebJars is import the webjars-play helper library in your build.sbt:

org.webjars" %% "webjars-play" % "2.4.0-1"

I found it very helpful as it allows you to dynamically locate the libraries you will import. To use this feature, you need to add a new line to your routes file:

GET     /webjars/*file          

At this point we’re ready to import React in our build.sbt file. As simple as adding

org.webjars" % "react" % "0.13.3"

React recommends writing your code in JSX, which is an abstraction of Javascript. It is statically typed and mostly type-safe. JSX code is then precompiled to Javascript and ran as any other .js file. If you don’t do the precompilation on your server, it will be automagically done in the browser, but this will lead to a runtime warning and performance deterioration. In order to enable the server-side precompilation, we need to include the sbt-react plugin to our project. Open the file plugins.sbt in your project folder and add

addSbtPlugin("com.github.ddispaltro" % "sbt-reactjs" % "0.5.2")

Go back to build.sbt and enable the SbtWeb plugin by adding it next to the Play plugin:

lazy val root = (project in file(".")).enablePlugins(PlayScala, SbtWeb)

Note: after changes in build.sbt or plugins.sbt, you most likely need to reload the project; the simplest way is to use the reload command from the sbt console. Otherwise, just close and rebuild the project from command line (that is, launch activator in the project folder and then clean and compile).

Now we’re all set to start following the Facebook tutorial. Create your own view in the views package or modify the existing index.scala.html. Whichever you choose, add the react.js library. It should look like this:

<!DOCTYPE html>
    <script type='text/javascript' src='"react", "react.js"))'></script>
    <div id="content"></div>

Note the .fullpath call in the react inclusion. This is needed as there are two instances of react.js in the React library, so we need to specify its position to the locator; see this question on StackOverflow. As my personal advice, use single quotes in the <script> tags; double quotes might mess up your paths.

Proceed with the tutorial. When the moment comes to create your JSX file, create first a new package assets inside the package app and a package javascripts under assets. app.assets.javascripts is where you’ll store the JSX file you will reference from your HTML file. I called it reactTest.jsx (note the .jsx extension), but from the point of view of the HTML file, you need to consider the translation to javascript. Therefore, our inclusion will be

<script type='text/javascript' src='@routes.Assets.versioned("javascripts/reactTest.js")'></script>

and not

<script type='text/jsx' src='@routes.Assets.versioned("javascripts/reactTest.jsx")'></script>

Also, you will need to include this file after the definition of your “content” div. This is because the content of such script will resolve directly in DOM elements. Including this file in the <head> section would result in a runtime error. Our <body> will look like this:

    <div id="content"></div>
    <script type='text/javascript' src='@routes.Assets.versioned("javascripts/reactTest.js")'></script>

Proceed with the tutorial. Don’t forget to run your server in between steps to check how it is going!

At some point, the tutorial will point you to the marked.js library, which is able to parse MarkDown straight from your Javascript (JSX) file. Nothing easier, now that we know how to work with WebJars. In order to find if there is a WebJar available, check directly on the WebJar website. After finding out, include it into your build.sbt file:

org.webjars" % "marked" % "0.3.2"

and reference it from your HTML file as

<script type='text/javascript' src='"marked.js"))'></script>

As you code through, at some point it will ask you to generate content from a server. We’re working with Play, so again: nothing easier! Add an endpoint in the routes file

GET     /comments                   controllers.Application.comments

and the corresponding data source and endpoint in Application.scala:

// Initialise the comments list
var commentsJson: JsArray = Json.arr(
  Json.obj(JSON_KEY_AUTHOR -> "Pete Hunt", JSON_KEY_TEXT -> "This is one comment"),
  Json.obj(JSON_KEY_AUTHOR -> "Jordan Walke", JSON_KEY_TEXT -> "This is *another* comment")

// Returns the comments list
def comments = Action {

This is also when you are required to reference jQuery. Like for the other libraries, add to your build.sbt file

"org.webjars" % "jquery" % "2.1.4"

and to the HTML file the following:

<script type='text/javascript' src='"jquery.js"))'></script>

From your JSX code, point here when this data is needed. Assuming you’re running locally, the url will be http://localhost:9000/comments. Later on, when you’ll need to implement the server-side logic to add a comment to the list, you can create an endpoint like this

POST    /comment                    controllers.Application.comment(author, text)

and the code in Application.scala:

// Adds a new comment to the list and returns it
def comment(author: String, text: String) = Action {
  val newComment = Json.obj(
    JSON_KEY_AUTHOR -> author,
    JSON_KEY_TEXT -> text)
  commentsJson = commentsJson :+ newComment

The Ajax call to this from your JS file will look like this:

var commentUrl = "http://localhost:9000/comment?author=" + author + "&text=" + text;
  url: commentUrl,
  method: 'POST',
  dataType: 'json',
  cache: false,
  success: function(data) {
  error: function(xhr, status, err) {
    console.error(commentUrl, status, err.toString());

Finish the tutorial and your service will be complete. Modular and reactive like never before! The code for this project is available here on GitHub.

Last modified: 3 July 2015