Let’s do a quick Express.js “Hello World” from scratch.

 

Install Node.js

First, make sure Node.js is installed.

Check:

node -v
npm -v

👉 If not installed, download from nodejs.org (LTS version).

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2️⃣ Create a new project

mkdir express-hello
cd express-hello

Initialize npm:

npm init -y

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3️⃣ Install Express.js

npm install express

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4️⃣ Create

index.js

Create a file named index.js and add this code:

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

const PORT = 3000;

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(PORT, () => {
  console.log(`Server running at http://localhost:${PORT}`);
});

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5️⃣ Run the server

node index.js

You’ll see:

Server running at http://localhost:3000

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6️⃣ Open in browser

Go to 👉 http://localhost:3000

🎉 Output:

Hello World!

---

(Optional) Auto-restart with nodemon

For development:

Go to 👉 https://www.npmjs.com/

Search nodemon pakage

npm -i nodemon

Update package.json:

"scripts": {
  "start": "node index.js",
  "dev": "nodemon index.js"
}

Run:

npm run dev

🔹 What is Routing in Express?

Routing decides how your app responds to a client request (URL + HTTP method).

👉 Syntax:

app.METHOD(PATH, HANDLER)

Example:

app.get('/users', (req, res) => {
  res.send('Users list');
});

---

1️⃣ Basic Routes

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

app.get('/', (req, res) => {
  res.send('Home Page');
});

app.post('/login', (req, res) => {
  res.send('Login API');
});

app.put('/user', (req, res) => {
  res.send('Update User');
});

app.delete('/user', (req, res) => {
  res.send('Delete User');
});

app.listen(3000);

---

2️⃣ Route Parameters (Dynamic Routes)

Used when data comes from URL.

app.get('/user/:id', (req, res) => {
  res.send(`User ID: ${req.params.id}`);
});

URL:

/user/101

Output:

User ID: 101

Multiple params:

app.get('/post/:category/:id', (req, res) => {
  res.json(req.params);
});

---

3️⃣ Query Parameters

Used for filters, pagination, search.

app.get('/search', (req, res) => {
  res.json(req.query);
});

URL:

/search?keyword=node&page=2

---

4️⃣ Route Handlers (Multiple Callbacks)

app.get(
  '/profile',
  (req, res, next) => {
    console.log('Middleware');
    next();
  },
  (req, res) => {
    res.send('Profile Page');
  }
);

---

5️⃣ Express Router (Best Practice)

Use Router to organize routes (like modules in Drupal).

📁 Folder structure

project/
 ├─ routes/
 │   └─ users.js
 ├─ app.js

routes/users.js

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

router.get('/', (req, res) => {
  res.send('All Users');
});

router.get('/:id', (req, res) => {
  res.send(`User ${req.params.id}`);
});

router.post('/', (req, res) => {
  res.send('Create User');
});

module.exports = router;

app.js

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

const userRoutes = require('./routes/users');

app.use('/users', userRoutes);

app.listen(3000);

URLs:

GET /users
GET /users/1
POST /users

---

6️⃣ Route Grouping

app.route('/book')
  .get((req, res) => res.send('Get book'))
  .post((req, res) => res.send('Add book'))
  .put((req, res) => res.send('Update book'));

---

7️⃣ Middleware in Routing

const auth = (req, res, next) => {
  console.log('Auth checked');
  next();
};

app.get('/dashboard', auth, (req, res) => {
  res.send('Dashboard');
});

---

8️⃣ 404 Route Handling

Always keep at the bottom 👇

app.use((req, res) => {
  res.status(404).send('Route not found');
});

---

9️⃣ REST API Example (Real World)

router.get('/', (req, res) => res.json({ action: 'list' }));
router.post('/', (req, res) => res.json({ action: 'create' }));
router.get('/:id', (req, res) => res.json({ action: 'view', id: req.params.id }));
router.put('/:id', (req, res) => res.json({ action: 'update', id: req.params.id }));
router.delete('/:id', (req, res) => res.json({ action: 'delete', id: req.params.id }));