I want to send data that is from serialport to client by SSE

[3210439]

hello I'm trying to send data that is from serialport to client by SSE but, getting data from serialport is work and SSE(server-sent-events) is also work but, when I sent data that is from serialport that value was '' but console.log say has value '123.0g like this
this is my cord can you help me?

`
const express = require("express");
const cors = require("cors");
const liveStreamApp = express();

liveStreamApp.use(cors());
const clients = {};

// @todo: This server should receives msgs from AMQPCloud

const { SerialPort, ReadlineParser } = require('serialport')
const port = new SerialPort({ path: 'COM5', baudRate: 2400 })
let str = '';
let weight = '';

port.on('readable', function () {
let a = port.read().toString('ascii');
str += a;
if (a === 'g') {
//console.log(str);
if (str.includes('WTST')) {
weight = str;

        Object.keys(clients).forEach(client => {
            console.log(`Sending msg to ${client}...`);
            clients[client].write(`event: walletChange\n`);
            clients[client].write(`data: ` + weight + `\n\n`);
        })
    }
    str = '';
}

})

liveStreamApp.get('/wallet', async (req, res) => {
const client = req.query.client;
clients[client] = res; // save response in memory
console.info(Registered: ${client})
// remove client when disconnect
res.socket.on('end', e => {
delete clients[client];
console.info(Unregistered: ${client})
res.end();
});
// accept SSE stream
res.setHeader("Content-Type", "text/event-stream");
// send welcome msg
res.write(event: walletChange\n);
res.write(data: Hello ${client}, you will receive updates when available...\n\n);
})

setInterval(_ => {
// send balance to registered clients every 10s || when needed
Object.keys(clients).forEach(client => {
console.log(Sending msg to ${client}...);
clients[client].write(event: walletChange\n);
//clients[client].write(data: Your balance ${client}!\n\n);
//clients[client].write(data: + weight);
//clients[client].write(data: + str);
//console.log(weight);
})
}, 1500)

liveStreamApp.listen(1979, _ => console.info(listening on 1979...));
`