After we have configured our AWS IoT and added the IoT device, we can develop a program to access AWS IoT. In this scenario, our computer is used as an IoT thing. We also used Node.js to access AWS IoT, so we need to install AWS IoT SDK for JavaScript. For testing, we will build a Node.js application to access AWS IoT for such purposes as connecting, sending, and receiving.

Now, create a file called comp-demo.js. Then, write the following Node.js scripts:

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

Please change the path and certificate files from your AWS IoT on parameters such as keyPath, certPath, caPath, host, and region. Save this file.

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());
});