Now we will review our program, comp-demo.js. The following is a list of steps for the program:

1. Firstly, we apply the required library from AWS IoT SDK for JavaScript. Then, we declare our device based on our IoT thing from AWS IoT:

var awsIot = require('aws-iot-device-sdk');
var device = awsIot.device({
    keyPath: 'cert/macos-computer.private.key',
   certPath: 'cert/macos-computer.cert.pem',
     caPath: 'cert/root-CA.crt',
       host: 'xxxxxxx.iot.ap-southeast-1.amazonaws.com',
   clientId: 'user-testing',
     region: 'ap-southeast-'
 });

2. We try to connect to AWS IoT. After we are connected, we subscribe a specific topic, for instance, topic_1. Then, we send a message by calling the publish() function:

device
   .on('connect', function() {
     console.log('connected');
     device.subscribe('topic_1');
     device.publish('topic_1', JSON.stringify({ test_data: 1}));
   });

3. To receive an incoming message from AWS IoT, we listen to the message event as follows:

device
   .on('message', function(topic, payload) {
     console.log('message', topic, payload.toString());
});