React js - nodemon：应用程序崩溃 - 在启动之前等待文件更改

Question

I just started using nodemon and strtaed creating a very small example project. However, as soon as I launch the server sudo npm run dev I get the following error:

[nodemon] app crashed - waiting for file changes before starting...

The error says that there is a mistake on users.js:7 app.use(expressLayouts);

emanuele@pc:~/Desktop/dashboard$ sudo npm run dev

dashboard@1.0.0 dev /home/emanuele/Desktop/dashboard nodemon app.js

[nodemon] 2.0.2 [nodemon] to restart at any time, enter rs [nodemon] watching dir(s): . [nodemon] watching extensions: js,mjs,json [nodemon] starting node app.js /home/emanuele/Desktop/dashboard/routes/users.js:7 app.use(expressLayouts); ^

ReferenceError: app is not defined at Object. (/home/emanuele/Desktop/dashboard/routes/users.js:7:1) at Module._compile (internal/modules/cjs/loader.js:955:30) at Object.Module._extensions..js (internal/modules/cjs/loader.js:991:10) at Module.load (internal/modules/cjs/loader.js:811:32) at Function.Module._load (internal/modules/cjs/loader.js:723:14) at Module.require (internal/modules/cjs/loader.js:848:19) at require (internal/modules/cjs/helpers.js:74:18) at Object. (/home/emanuele/Desktop/dashboard/app.js:7:19) at Module._compile (internal/modules/cjs/loader.js:955:30) at Object.Module._extensions..js (internal/modules/cjs/loader.js:991:10) [nodemon] app crashed - waiting for file changes before starting...

So below is where the error should be:

app.js

const express = require('express');
const expressLayouts = require('express-ejs-layouts');

const app = express();

app.use(expressLayouts);
app.set('view engine', 'ejs');

// Routes
app.use('/', require('./routes/index'));
app.use('/users', require('./routes/users'));

const PORT = process.env.PORT || 5000;

app.listen(PORT, console.log(`Server started on port ${PORT}`));

index.js

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

router.get('/', (req, res) => res.render('welcome'));

module.exports = router;

users.js

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

// Login Page
router.get('/login', (req, res) => res.send('Login'));

// Register Page
router.get('/register', (req, res) => res.send('Register'));

module.exports = router;

If needed below my package.json

{
    "name": "dashboard",
    "version": "1.0.0",
    "description": "",
    "main": "app.js",
    "scripts": {
        "start": "node app.js",
        "dev": "nodemon app.js"
    },
    "keywords": [],
    "author": "",
    "license": "ISC",
    "dependencies": {
        "bcryptjs": "^2.4.3",
        "connect-flash": "^0.1.1",
        "ejs": "^3.0.1",
        "express": "^4.17.1",
        "express-ejs-layouts": "^2.5.0",
        "express-session": "^1.17.0",
        "mongoose": "^5.8.11",
        "passport": "^0.4.1",
        "passport-local": "^1.0.0"
    },
    "devDependencies": {
        "nodemon": "^2.0.2"
    }
}

I don't understand what is wrong in the above piece of code. I consulted some posts such as:

1) This but could't solve the problem

2) This one too but no success

3) I consulted this source

4) I came across this too but could still not figure out what could be wrong

Thanks for pointing in the right direction to understand where the error could be.

Answer 1

Inside index.js (and users.js ) there is no app variable defined:

app.use(expressLayouts);
app.set('view engine', 'ejs');

These should be defined in app.js where you have this definition const app = express(); . They will then apply for all other routes in your Express application, so defining them multiple times is not needed.