Adding real time using Socket.IO

Using the socket.IO library, create a simple real-time widget with Ubidots and the HTML Canvas.

Socket.IO is a JS library easy to implement that manages socket connections and messages, thus enabling a bi-directional real-time connection protocol. Ubidots has implemented this real-time protocol within its core servers to easily update devices, to retrieve and store data inside any JS variable, and without the need to implement any requests, using sockets.

The following shows how to create a HTML Canvas Widget which will display a variables' data in a real time fashion. This example relies on the previous Create an LCD screen with the HTML Canvas, so please head to said section first.

Create the HTML element in which the data will be displayed:

<p id="content"></p>

Add the logic of the widget by using the following JavaScript code:

var socket;
var srv = window.location.hostname + ":443"; //this allows the widget to work at the white label level
var VAR_ID = "variable-id"; // Put here your var Id
var TOKEN = "YOUR-TOKEN"  // Put here your token
$(document).ready(function () {
    // Implements the connection to the server
    socket = io.connect("https://" + srv, { path: '/notifications' });
    var subscribedVars = [];

    // Function to publish the variable ID
    var subscribeVariable = function (variable, callback) {
        // Publishes the variable ID that wishes to listen
        socket.emit('rt/variables/id/last_value', {
            variable: variable
        });
        // Listens for changes
        socket.on('rt/variables/' + variable + '/last_value', callback);
        subscribedVars.push(variable);
    };

    // Function to unsubscribed for listening
    var unSubscribeVariable = function (variable) {
        socket.emit('unsub/rt/variables/id/last_value', {
            variable: variable
        });
        var pst = subscribedVars.indexOf(variable);
        if (pst !== -1) {
            subscribedVars.splice(pst, 1);
        }
    };

    var connectSocket = function () {

        // Implements the socket connection
        socket.on('connect', function () {
            socket.emit('authentication', { token: TOKEN });
        });
        window.addEventListener('online', function () {
            socket.emit('authentication', { token: TOKEN });
        });
        socket.on('authenticated', function () {
            subscribedVars.forEach(function (variable_id) {
                socket.emit('rt/variables/id/last_value', { variable: variable_id });
            });
        });
    }

    /* Main Routine */

    connectSocket();
    // Should try to connect again if connection is lost
    socket.on('reconnect', connectSocket);

    // Subscribe Variable with your own code.
    subscribeVariable(VAR_ID, function (value) {
        var parsedValue = JSON.parse(value);
        console.log(parsedValue);
        $('#content').text(value);
    })
});

The following 3rd party libraries will be needed:

https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js
https://iot.cdnedge.bluemix.net/ind/static/js/libs/socket.io/socket.io.min.js

The following is the result: