How to properly send and receive "POST" requests to and from a server

I am trying to make a server for a website. The server works perfectly, and it can receive and send data normally. I have hosted the server, and I made a demo client-side repl on Replit to test the flow. But somehow, either the reply isn't receiving or sending properly, or the server isn't working. (For the client-side code, I am using JQuery)

// Client Side Code
const url = "My url";
const data = {
    "file": "lol.html"
}

function start() {
    console.log("test 1")
    $.post(url, data, function(data, status) {
        console.log(data + "is data & status is " + status);
    });
}

// Server-side code
var http = require('http'); // Import Node.js core module
var fs = require('fs'); // File System
var url = require('url');

var server = http.createServer(function(req, res) {   //create web server
    if (req.url == '/') { //check the URL of the current request

        res.writeHead(200, { 'Content-Type': 'application/json' });
        res.write(JSON.stringify({ message: "This is the Backend server for my website" }));
        res.end();

    }
    else if (req.url == "/ping") {

        res.writeHead(200, { 'Content-Type': 'application/json' });
        res.write(JSON.stringify({ message: "Pong!" }));
        res.end();

    }
    else if (req.url.startsWith("/read")) {

        var q = url.parse(req.url, true);
        var qdata = q.query;
        fs.readFile(String(qdata.file), function(err, data) {
            if (err) {
                res.writeHead(404, { 'Content-Type': 'text/html' });
                return res.end("404 Not Found");
            }
            res.writeHead(200, { 'Content-Type': 'text/html' });
            res.write(data);
            return res.end();
        });
    }
    else if (req.url.startsWith("/get")) {

        var q = url.parse(req.url, true);
        var qdata = q.query;
        fs.readFile(String(qdata.file), function(err, data) {
            if (err) {
                res.writeHead(404, { 'Content-Type': 'text/html' });
                return res.end("404 Not Found");
            }
            res.writeHead(200, { 'Content-Type': 'text/html' });
            res.write(data);
            return res.end();
        });
    }
    else {
        res.end('Invalid Request!');
    }

});

server.listen(5000); //6 - listen for any incoming requests

console.log('Node.js web server at port 5000 is running..')

Can Someone tell me how to perform this properly?