Port number showing in Nodejs express folder listing - node.js

Question

I have a node js express application which is running on port 3000. when i ran it first it worked. Then when i ran it for the second time, it says the "port is already in use". I have checked all the running ports and also searched by specific 3000 port, but still cannot find a process running on 3000 port.
Then i changed the port to 3002 and checked, now the program ran. And when i closed and ran it again, it says "port is already in use".
Same is the case when i tried with port 3003.
i tried the below to check for the running ports
sudo lsof -i -P -n | grep LISTEN
netstat -an | grep 3000
lsof -i:3000
kill <PID>
Afterwards i noticed that when i did a folder listing it showed the folder "3000", "3002", "3003" as folder/file. I don't know what this is.
below is my www file
#!/usr/bin/env node
/**
* Module dependencies.
*/
var app = require('../app');
var debug = require('debug')('mqtt-node:server');
var http = require('http');
/**
* Get port from environment and store in Express.
*/
var port = normalizePort(process.env.PORT || '3001');
app.set('port', port);
/**
* Create HTTP server.
*/
var server = http.createServer(app);
/**
* Listen on provided port, on all network interfaces.
*/
server.listen(port);
server.on('error', onError);
server.on('listening', onListening);
/**
* Normalize a port into a number, string, or false.
*/
function normalizePort(val) {
var port = parseInt(val, 10);
if (isNaN(port)) {
// named pipe
return val;
}
if (port >= 0) {
// port number
return port;
}
return false;
}
/**
* Event listener for HTTP server "error" event.
*/
function onError(error) {
if (error.syscall !== 'listen') {
throw error;
}
var bind = typeof port === 'string'
? 'Pipe ' + port
: 'Port ' + port;
// handle specific listen errors with friendly messages
switch (error.code) {
case 'EACCES':
console.error(bind + ' requires elevated privileges');
process.exit(1);
break;
case 'EADDRINUSE':
console.error(bind + ' is already in use');
process.exit(1);
break;
default:
throw error;
}
}
/**
* Event listener for HTTP server "listening" event.
*/
function onListening() {
var addr = server.address();
var bind = typeof addr === 'string'
? 'pipe ' + addr
: 'port ' + addr.port;
debug('Listening on ' + bind);
}
Could anyone help me with why the ran port numbers are showing in the folder listing and also i cannot find any running node ports, but still says the port is already in use.

Answer 1

I made a change in my env file and the issue is resolved. I had defined the port in my .env as PORT="3000" and i changed to PORT=3000, and it works.
I am not sure why PORT="3000" was working in my PC and not in my server. This is why i was not focusing on this factor.