DukeScript with Node.js backend

In one of our latest projects the customer has decided to use Node.js as a backend. So we decided to share a minimal demo how simple it is using DukeScript APIs.

You’ll need node installed and in addition the websocket module. Here’s the server, we’re using a websocket to make it a little fancier.

var ipaddress = 'localhost';
var port = 8085;

const WebSocket = require('ws');

var WebSocketServer = WebSocket.Server
  , wss = new WebSocketServer({host:ipaddress, port:port});

wss.broadcast = function(data) {
  wss.clients.forEach(function each(client) {
    if (client.readyState === WebSocket.OPEN) {
        console.log('send response');

wss.on('connection', function (ws) {
    ws.on('message', function (message) {
        console.log('received message ' + message);
        wss.broadcast("{message: 'message from server'}");
        setInterval(function () {
            wss.broadcast("{message: 'message "+i+" from server'}");
        }, 5000);

The websocket server sends a simple JSON message every 5 seconds after we connected. Don’t worry too much about the server code. This is just for demo purposes. Now we need a Java model to read the message:

@Model(className = "Data", targetId = "", instance = true, properties = {
    @Property(name = "message", type = String.class)
final class DataModel {

DukeScript has the extremely convenient @OnReceive annotation, that takes care of serializing messages to and deserializing messages from the server. So we extend our class with:

@OnReceive(url = "ws://localhost:8085", data = Data.class, method = "WebSocket")
public static void receive(Data data, Data message) {
    if (message != null) {
    } else { // null means: connection established
        System.out.println("conection established");

This will generate a method in our Model class with all the boilerplate code. To establish the connection you once call the method with a null argument.

private static Data ui;
static void onPageLoad() throws Exception {
    ui = new Data("Hallo");
    ui.receive(null); //connect

After that you can call the receive method with data to send and receive messages via the websocket. The websocket can also push back messages to you. Let’s add a @Function, so we can send a message from the UI:

public static void send(Data data) {

Now we only need a UI to start the connection, so we add this to our View:

<input type="text" data-bind="textInput: message">
<button data-bind="click: send">Send Message</button>

The full code to play with is available on Github.

And if you want to code the Node based server in Java as well, have a look at this project: Node4J.

That’s it. Easy, isn’t it? Have fun coding DukeScript!