Error: "ReferenceError: app is not defined" [closed]

Getting:

ReferenceError: app is not defined.

Here is the error details:

\[nodemon\] restarting due to changes...
\[nodemon\] starting `node server.js`

D:\\ebl\\server\\app\\routes.js:4
app.get('/health', (\_req, res) =\> {
^

ReferenceError: app is not defined
at Object.\<anonymous\> (D:\\ebl\\server\\app\\routes.js:4:1)
at Module.\_compile (node:internal/modules/cjs/loader:1241:14)
at Module.\_extensions..js (node:internal/modules/cjs/loader:1295:10)
at Module.load (node:internal/modules/cjs/loader:1091:32)
at Module.\_load (node:internal/modules/cjs/loader:938:12)
at Module.require (node:internal/modules/cjs/loader:1115:19)
at require (node:internal/modules/helpers:130:18)
at Object.\<anonymous\> (D:\\ebl\\server\\app\\app.js:8:9)
at Module.\_compile (node:internal/modules/cjs/loader:1241:14)
at Module.\_extensions..js (node:internal/modules/cjs/loader:1295:10)

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

Source code:
app.js

require('dotenv').config('../.env')
const express = require('express')
const app = express();

app.use(require('./middleware'));
app.use(require('./routes'));
app.use(require('./error'));

module.exports = app;

routes.js

 const router = require('express').Router();

 app.get('/health', (_req, res) => {
 res.status(200).json({ message: 'success' })
 });

 module.exports = router

package.json

{
  "name": "ebl",
  "version": "1.0.0",
  "description": "ebl",
  "main": "index.js",
  "scripts": {
    "dev": "nodemon server.js"
  },
  "keywords": [],
  "author": "ebl",
  "license": "ISC",
  "dependencies": {
    "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 chanage the path route '/health' to another name '/home', but error is the same