Using nodemon Server Listining on port: 4000 but finally [nodemon] app crashed

Question

When I am trying to run the application, then the Server Listining & Database Connected Successfully but App is crashed directly.

Could not get any response at http://localhost:4000/

Here is the full error, nodemon version is 3.1.0

[nodemon] starting `node server.js`
Server Listining on port: 4000
Database Connected Successfully
node:events:492
      throw er; // Unhandled 'error' event
      ^

Error: listen EADDRINUSE: address already in use :::4000
    at Server.setupListenHandle [as _listen2] (node:net:1872:16)
    at listenInCluster (node:net:1920:12)
    at Server.listen (node:net:2008:7)
    at Function.listen (D:server\node_modules\express\lib\application.js:635:24)
    at D:\server\server.js:25:13
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
Emitted 'error' event on Server instance at:
    at emitErrorNT (node:net:1899:8)
    at process.processTicksAndRejections (node:internal/process/task_queues:82:21) {
  code: 'EADDRINUSE',
  errno: -4091,
  syscall: 'listen',
  address: '::',
  port: 4000
}

Node.js v20.9.0
[nodemon] app crashed - waiting for file changes before starting...

server.js full source code

const express = require('express');
const app = express();

const connectDB = require('./db/db');

app.get('/', (req, res) => {
    const obj = {
        name: 'jam',
        email: '[email protected]'
    }
    res.json(obj);
})

PORT = 4000;
app.listen(PORT, () => {
    console.log(`Server Listining on port: ${PORT}`)
})

connectDB(`mongodb://localhost:27017/attendance-db`)
    .then(() => {
        console.log('Database Connected Successfully');
        app.listen(PORT, () => {
            console.log(`Database Listining on port: ${PORT}`)
        })
    })
    .catch((e) => console.log(e))

package.json

{
  "name": "elb",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "dev": "nodemon server.js"
  },
  "keywords": [],
  "author": "elb",
  "license": "ISC",
  "dependencies": {
    "bcryptjs": "^2.4.3",
    "cors": "^2.8.5",
    "dotenv": "^16.4.5",
    "express": "^4.19.2",
    "mongoose": "^8.3.5",
    "morgan": "^1.10.0"
  },
  "devDependencies": {
    "nodemon": "^3.1.0"
  }
}

I changed the PORT several time but result is the same

Thank you for your time

Answer 1

Error: listen EADDRINUSE: address already in use :::4000

It clearly means that you have already connected the PORT to 4000 and you are again trying to connect the same PORT.

You just need to remove a section of code from server.js that you have defined after PORT = 4000;

just remove it from server.js.The issue will be resolved.

app.listen(PORT, () => {
    console.log(`Server Listining on port: ${PORT}`)
})

Remove only the mentioned code not the PORT where you assigned 4000 just before the above mentioned code.Try this.