What is Backend Development?

The Big Picture#

When you use an app, you see buttons, forms, and pretty interfaces. That's the frontend - what users interact with.

But where does the data come from? Where are your login credentials stored? Who checks if your password is correct? That's the backend - the brain behind the scenes.

Frontend vs Backend#

┌─────────────────────────────────────────────────────────────────┐
│                         User's Browser                          │
│  ┌───────────────────────────────────────────────────────────┐  │
│  │                      FRONTEND                             │  │
│  │  • What you see (HTML, CSS)                               │  │
│  │  • Interactions (JavaScript)                              │  │
│  │  • Runs in the browser                                    │  │
│  └───────────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────────┘
                              │
                              │ HTTP Requests
                              │ (Get data, send forms)
                              ▼
┌─────────────────────────────────────────────────────────────────┐
│                          Server                                  │
│  ┌───────────────────────────────────────────────────────────┐  │
│  │                      BACKEND                              │  │
│  │  • Business logic (rules, calculations)                   │  │
│  │  • Data storage (databases)                               │  │
│  │  • Security (authentication, authorization)               │  │
│  │  • Runs on a server                                       │  │
│  └───────────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────────┘

What Backend Developers Do#

1. Build APIs (Application Programming Interface)#

APIs are how frontend and backend talk. When you click "Login", the frontend sends your credentials to a backend API:

// Frontend sends request
fetch('/api/login', {
  method: 'POST',
  body: JSON.stringify({ email: 'user@example.com', password: '123456' })
})

// Backend receives and responds
app.post('/api/login', (req, res) => {
  const { email, password } = req.body;
  // Check credentials
  // Return success or error
  res.json({ success: true, token: 'abc123' });
});

2. Store and Retrieve Data#

Users create accounts, post photos, write messages. All this data lives in databases:

// Save a new user
const user = await User.create({
  email: 'user@example.com',
  name: 'John Doe'
});

// Find all posts by a user
const posts = await Post.find({ userId: user.id });

3. Handle Business Logic#

Rules that make the app work:

• Can this user view this content? (permissions)
• Is this coupon code valid? (validation)
• Calculate shipping cost based on weight and destination
• Send an email when order ships

// Business logic example
function calculateOrderTotal(items, couponCode) {
  let total = items.reduce((sum, item) => sum + item.price, 0);

  if (couponCode === 'SAVE20') {
    total = total * 0.8; // 20% off
  }

  if (total > 100) {
    total = total - 10; // Free shipping over $100
  }

  return total;
}

4. Secure the Application#

• Hash passwords (never store plain text)
• Verify users are who they claim to be
• Protect against attacks (SQL injection, XSS)
• Rate limiting (prevent spam/abuse)

// Hash password before saving
const hashedPassword = await bcrypt.hash(password, 10);

// Verify password on login
const isValid = await bcrypt.compare(inputPassword, hashedPassword);

5. Integrate with External Services#

• Payment processors (Stripe, PayPal)
• Email services (SendGrid, AWS SES)
• Cloud storage (S3, Cloudinary)
• Third-party APIs (Google Maps, Twilio)

// Send email through external service
await sendgrid.send({
  to: user.email,
  subject: 'Order Confirmation',
  text: `Your order #${order.id} has been confirmed!`
});

How Web Requests Work#

When you type a URL or click a button:

1. Browser makes HTTP request
   GET https://api.example.com/users

2. Server receives request
   • Parses URL, method, headers, body
   • Authenticates user (if needed)

3. Server processes request
   • Runs business logic
   • Queries database
   • Calls external services

4. Server sends response
   {
     "data": [
       { "id": 1, "name": "Alice" },
       { "id": 2, "name": "Bob" }
     ]
   }

5. Browser receives response
   • Frontend displays data to user

Backend vs Full-Stack#

Common Backend Tasks#

Here's what a typical backend developer might do in a day:

1. Add a new API endpoint - Create /api/products/search to search products
2. Fix a bug - Users can't update their profile picture
3. Improve performance - Add caching to slow database queries
4. Security update - Patch a vulnerability in a dependency
5. Write tests - Ensure the checkout flow works correctly
6. Deploy - Push new features to production

What You'll Learn in This Guide#

This guide takes you from zero to building production-ready backends:

1. Fundamentals - How Node.js and JavaScript work on servers
2. APIs - Build RESTful endpoints with Express.js
3. Databases - Store data with MongoDB and Redis
4. Authentication - Secure user login and sessions
5. Testing - Write tests to catch bugs
6. Deployment - Get your app running in production

Key Takeaways#

1. Backend = server-side - Code that runs on servers, not browsers
2. APIs connect everything - Frontend talks to backend through APIs
3. Databases store data - Users, posts, orders, everything
4. Security is critical - Protect user data and prevent attacks
5. Logic lives here - Business rules, calculations, integrations

Ready to start? Let's look at choosing the right language and framework for your backend.