send serial port data to front-end with express & node - express

Question

I want to send serial port data to a browser UI with express. So far my code looks like this:
var SerialPort = require("serialport");
var serialport = new SerialPort("/dev/cu.usbmodem1421");
var express = require('express');
var app = express();
var datenFromA;
serialport.on('open', function(){
console.log('Serial Port Opend');
serialport.on('data', function(data){
datenFromA = data[0];
console.log(datenFromA);
});
});
app.get('/', function (req, res) {
res.send('Hello World')
})
app.listen(3000);
Instead of the 'Hello World' I want to send the value of variable datenFromA to the browser. Any ideas how to pass the value to the app.get function?
Thanks in advance.

Answer 1

Essentially you need to wait until you receive an event. Quick dirty example given below:
const SerialPort = require("serialport");
const serialport = new SerialPort("/dev/cu.usbmodem1421");
const express = require('express');
const app = express();
// Only need to do this once.
serialport.on('open', () => console.log('Serial Port Opend'));
app.get('/', async (req, res) => {
const promise = new Promise((resolve, reject) => {
serialport.on('data', (data, err) => {
if (err) {
reject(err);
return;
}
resolve(data[0]);
});
})
const data = await promise;
res.json(data);
})
app.listen(3000);