server.js

//var http = require('http'); // Import Node.js core module
var express = require('express');
var app = express();
const SerialPort = require('serialport'); //https://serialport.io/docs/guide-usage
const Readline = require('@serialport/parser-readline');

const port = new SerialPort('COM4', { baudRate: 9600 });
const parser = port.pipe(new Readline());// Read the port data
	
port.on("open", () => {
  console.log('serial port open');
});

// Open errors will be emitted as an error event
port.on('error', function(err) {
  console.log('Error: ', err.message)
})

parser.on('data', data =>{
  console.log(data);
});

app.get('/', function (req, res) {
	res.send('Hello world');
	port.write('testing testing hello ben\n', (err) => {
			if (err) {
			  return console.log('Error on write: ', err.message);
			}
		});
})

var server = app.listen(5000, function () {
	var host = server.address().address;
	var port = server.address().port;
	console.log("Node.js server running on port %s", port);
})