What is the “backend” in backend web development?

The backend refers to the part of a software application or website that handles the logic, database interactions, authentication, and server-side operations - essentially, everything that happens behind the scenes.

What Does “Logic” Mean in This Context?

Logic refers to the instructions and rules that define how the application behaves. This is often called business logic - the code that drives how data is processed and how the system responds.

💡 Examples of Backend Logic

🛒 In an E-commerce App:

• Calculating the total price of items in a shopping cart.
• Applying discounts or promotions.
• Checking if an item is in stock.
• Charging the user’s credit card using a payment API.
• Sending a confirmation email after a purchase.

👤 In a Social Media App:

• Making sure a user can’t follow themselves.
• Enforcing rate limits on how many posts a user can make per minute.
• Determining who sees which posts (e.g., privacy settings).
• Checking if a user is authenticated before posting.

🧠 In Code Form (Simple Example)

def calculate_total(cart_items):
    total = 0
    for item in cart_items:
        total += item['price'] * item['quantity']
    return total

This function is backend logic - it takes a list of items in a cart and calculates the total cost. The frontend would call this on the server to get a total, but the calculation happens behind the scenes.

What are the key components of the backend?

1. Server
2. Application Logic
3. Database
4. APIs (Application Programming Interfaces)
5. Authentication and Authorization
6. Security & Middleware

A machine (or cloud-based service) that listens for and processes requests from clients (like web browsers or mobile apps) is called a server.

🔊 What Does “Listening” Actually Mean?

When we say a server is listening, we mean:

• It’s actively monitoring a specific IP address and port number (e.g., 0.0.0.0:3000) for incoming connections.
• When a client (like a browser) sends a request to that address, the backend accepts and processes it.

🧠 Suppose you run a Node.js backend server

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

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

app.listen(3000, () => {
  console.log('Server is listening on port 3000');
});

In this code:

• app.listen(3000) means the server is listening on port 3000.
• When a browser visits http://localhost:3000, it sends a request.
• The backend receives this request, processes it, and responds.