node-server.js

var net = require('net');
var fs = require('fs');

var HOST = '127.0.0.1';
var PORT = 5204;

// Create a server instance, and chain the listen function to it
// The function passed to net.createServer() becomes the event handler for the 'connection' event
// The sock object the callback function receives UNIQUE for each connection
net.createServer(function(sock) {
    
    // We have a connection - a socket object is assigned to the connection automatically
    console.log('CONNECTED: ' + sock.remoteAddress +':'+ sock.remotePort);
    
    // Add a 'data' event handler to this instance of socket
    sock.on('data', function(data) {
        
        console.log('DATA ' + sock.remoteAddress + ': ' + data);
        // Write the data back to the socket, the client will receive it as data from the server
        sock.write('You said "' + data + '"');
        let gesture = data.toString();
        fs.appendFile("./input.txt", gesture, function(err) {
            if(err) {
                return console.log(err);
            }

            console.log("The file was saved!");
        }); 
        /////
    });
    
    // Add a 'close' event handler to this instance of socket
    sock.on('close', function(data) {
        console.log('CLOSED: ' + sock.remoteAddress +' '+ sock.remotePort);
    });
    
}).listen(PORT, HOST);

console.log('Server listening on ' + HOST +':'+ PORT);