Get HTTP request body data using Node.js - node.js

Question

The frontend is index.html:
axios.post('http://localhost:1337/', {
clientId: document.getElementById('clientId').value,
cmd: document.getElementById('cmd').value,
type: document.getElementById('type').value,
amt: document.getElementById('amt').value,
merchantRef: document.getElementById('merchantRef').value,
channel: document.getElementById('channel').value,
successUrl: document.getElementById('successUrl').value,
failureUrl: document.getElementById('failureUrl').value,
webhookUrl: document.getElementById('webhookUrl').value,
goodsName: document.getElementById('goodsName').value
})
.then(function (response) {
var json = response.data;
document.getElementById('sessionId').innerHTML = json['sessionId'];
SpiralPG.init(json['sessionId']);
})
.catch(function (error) {
console.log(error);
});
The backend is server.js:
http.createServer(async function (req, res) {
try {
res.setHeader('Access-Control-Allow-Origin', '*');
res.setHeader('Access-Control-Request-Method', '*');
res.setHeader('Access-Control-Allow-Methods', 'OPTIONS, GET, POST');
res.setHeader('Access-Control-Allow-Headers', '*');
const buffers = [];
for await (const chunk of req) {
buffers.push(chunk);
};
const data = Buffer.concat(buffers).toString();
saleSession(res, data);
}
catch (error) {
console.log(error);
}
}).listen(port);
something inside function saleSession(); in the server.js to get the data from frontend(if I hard code in here, there will be no error, but change to input data from frontend, there will be error):
var merchantRef = JSON.parse(data).merchantRef;
let bodyData =
{
'clientId': JSON.parse(data).clientId,
'cmd': JSON.parse(data).cmd,
'type': JSON.parse(data).type,
'amt': JSON.parse(data).amt,
'merchantRef': merchantRef,
'channel': JSON.parse(data).channel,
'successUrl': JSON.parse(data).successUrl,
'failureUrl': JSON.parse(data).failureUrl,
'webhookUrl': JSON.parse(data).webhookUrl,
'goodsName': JSON.parse(data).goodsName
}
I'm just copy the code in https://nodejs.dev/learn/get-http-request-body-data-using-nodejs, which is node.js office website. Why the output is:
SyntaxError: Unexpected end of JSON input
at JSON.parse (<anonymous>)
at saleSession (C:\Users\JoeChan\Desktop\my-nodejs2\server.js:41:28)
at Server.<anonymous> (C:\Users\JoeChan\Desktop\my-nodejs2\server.js:104:9)
at processTicksAndRejections (node:internal/process/task_queues:96:5)