Server is in running status but when tried to hit api it is giving Error: connect ECONNREFUSED 127.0.0.1:3000 in POSTMAN

I’m trying to separate app and server. It is running properly but when tried to hit "app.get(‘/’)" api it is giving Error: connect ECONNREFUSED 127.0.0.1:3000 in Postman even after changing required settings.

In connect.js (connectDByour text)

const mongoose = require('mongoose');
const color = require('colorette');

const connectDB = (url) => {
    try {
        return mongoose.connect(url, {
            useNewUrlParser: true,
            useUnifiedTopology: true,
        });
    } catch (error) {
        console.log(color.bgRed(error));
    }
};
module.exports = connectDB;

In server.js

const app = require('./app');
const http = require('http')

const port = process.env.PORT || 3000;
const connectDB = require("./database/connect");
const server = http.createServer(app);
const color = require('colorette');

// 👇️ handle uncaught exceptions
process.on('uncaughtException', function (err) {
    console.log(color.red(`Uncaught Exception Error Occurred ${err}`));
});

const startDB = async () => {
    try {
        await connectDB(process.env.MONGO_URL);
        console.log(color.blue(`DB server is connected`));
        server.listen(() => {
            console.log(color.blue(`Node server is running on port ${port}...`));
        })
    } catch (error) {
        console.log(color.red(`ERROR is ${error}`));
    }
};

startDB();

In app.js

require("dotenv").config();
const express = require("express");
const app = express();
const cors = require('cors')
const users = require("./routes/users");
app.use(cors());
app.use(express.json());

app.get('/', (req, res) => {
    res.status(200).json(`Hello World`);
})
app.use('a/user', users);
module.exports = app

On Terminal

> nodemon server.js

[nodemon] 3.0.1
[nodemon] to restart at any time, enter `rs`
[nodemon] watching path(s): *.*
[nodemon] watching extensions: js,mjs,cjs,json
[nodemon] starting `node server.js`
DB server is connected
Node server is running on port 3000...

In Postman

Error: connect ECONNREFUSED 127.0.0.1:3000
Proxy
id: "958df20d-86ee-40af-8d08-4c3274d302ca"
disabled: false
host: "127.0.0.1"
match: {…}
port: 3000
tunnel: false
authenticate: false
Request Headers
Content-Type: application/json
Cache-Control: no-cache
Postman-Token: 515bf6ca-1031-4198-8fda-9c0f99b55c83
Host: localhost:3000
Connection: keep-alive

Separation of app and server file in Express and Nodejs

>Solution :

You are trying to use express app instance from app.js as options for http.createServer(). It would not be a valid options object for createServer.

use express‘s built-in listen() method

const app = require('./app');
const http = require('http')

const port = process.env.PORT || 3000;
const connectDB = require("./database/connect");
const color = require('colorette');

// 👇️ handle uncaught exceptions
process.on('uncaughtException', function (err) {
    console.log(color.red(`Uncaught Exception Error Occurred ${err}`));
});

const startDB = async () => {
    try {
        await connectDB(process.env.MONGO_URL);
        console.log(color.blue(`DB server is connected`));
        app.listen(port, () => {
            console.log(color.blue(`Node server is running on port ${port}...`));
        })
    } catch (error) {
        console.log(color.red(`ERROR is ${error}`));
    }
};

startDB();