Post data in node web server -js //array methods are not allowed in server

Web Development
#1

also iam not able to access controll allow – body

server js
working on local data.json

working origin is diffrent port thas CORS used

const http = require('http');
const url = require('url');
const fs = require('fs');

http.createServer((req, res)=>{
    var q = url.parse(req.url, true);

    if (req.method == "OPTIONS"){ //Preflight
        console.log("hy");
        res.writeHead(204, {
            "Access-Control-Allow-Headers" : 'content-type, body',
            "Access-Control-Allow-Origin" : 'http://127.0.0.1:5500'
        });
        res.end();
    }
    else if(req.method == "GET"){
        if(q.pathname === "/xyz"){
            fs.readFile('data.json', (err, data)=>{ 
                res.writeHead(200, {
                    "Content-type": 'application/json',
                    "Access-Control-Allow-Origin" : 'http://127.0.0.1:5500'
                })
                res.write(data);
                res.end()
            });      
        }
    }
    else if(req.method == "POST"){
        res.writeHead(200, {
            "Content-type": 'application/json',
            "Access-Control-Allow-Origin" : 'http://127.0.0.1:5500'
        });
        const d = req.headers.body;
//first tell me it's wrong or write , i dont know so much  about web server


//adding value in json formate but if json is emapty its not puting and[] also not puting any , 
// my meaning of this is not following index 
//.push() method is not allowed 

        fs.appendFile('data.json',d, (err) => console.log(err))
        res.end()
    }
}).listen(8080, () => console.log(`Server started on port 8000`));

request post js

fetch ('http://localhost:8080/xyz', {
        method:"POST",
        headers:{
            'Content-type': 'application/json',
            "body":JSON.stringify({
                Name:"Hitesh",
                surName:"Chaudhary",
                age:23,
                userid:1,
                learning:["html","css","java_script", "MERN Stack"],
                batch:"21MAY03"
            })
        },
    })
    .then((getresponse)=>getresponse.json())
    .then((data)=>console.log(data))
    .catch((err)=>console.log("this error" +err));