Now one of the most crucial parts of this component to create a new file called app.js

Create app.js file

// Import necessary libraries
var express = require('express'); // Express.js for building the server
var bodyParser = require('body-parser'); // Body-parser for parsing the request body
var cors = require('cors'); // CORS for handling cross-origin requests

// Import the Google Cloud client library
const {PubSub} = require('@google-cloud/pubsub'); // Google Cloud Pub/Sub for real-time messaging

// Initialize Express.js
var app = express();
app.use(cors()); // Use CORS middleware

app.use(bodyParser.json()); // Use body-parser middleware to parse JSON request body
app.use(bodyParser.urlencoded({ extended: true })); // Parse URL-encoded bodies

// Initialize Google Cloud Pub/Sub client
const pubSubClient = new PubSub();

// Define your Google Cloud Pub/Sub topic
const topicName = '<Replace with your topic name>';

// Define POST route for '/saveData'
app.post('/saveData', function(req, res) {
    let data = req.body;
    // Convert data object to JSON string
    let dataString = JSON.stringify(data);

    // Function to publish message to Google Cloud Pub/Sub
    async function publishMessage() {
      try {
        // Convert string to buffer
        const dataBuffer = Buffer.from(dataString);
        // Publish buffer to Google Cloud Pub/Sub
        const messageId = await pubSubClient.topic(topicName).publish(dataBuffer);

        console.log(`Message ${messageId} published.`);
        res.status(200).json({message: 'Data published successfully'});

      } catch (error) {
        console.error(`Received error while publishing: ${error.message}`);
        // Send error response
        res.status(500).json({message: 'Internal Server Error', error: error});
      }
    }
    // Call the publish function
    publishMessage().catch(console.error);
});

// Define GET route for '/'
app.get('/', function(req, res) {
    res.send('Hello, World! Welcome');
});

// Start the server
app.listen(3000, function() {
  console.log('Server listening on port 3000');
});