Day 12: Setting up an Express Server + Basic Routes

🧠 What You Will Learn Today

• What is a server?

• Why do we use Express?

• How to create an Express server?

• What are routes in Express?

• Real-life example: Build a mini product API

• Step-by-step code explanation

• FAQs

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🖥️ What Is a Server?

A server is just a computer (or code) that listens for requests and responds with data.

In web development:

• Client = Browser / Frontend (React, etc.)

• Server = Backend (Node.js + Express)

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💡 Why Use Express for Server?

Without Express, you have to write a lot of code to:

• Handle routes

• Parse data

• Send responses

But with Express.js, you can write clean, fast code for:
✅ APIs
✅ Middlewares
✅ Error handling
✅ Route handling

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🛠️ Let's Build: Product API (Basic Express Server)

We’ll create a simple API with 3 routes:

• / → Home route

• /products → All products

• /about → About page

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📁 Project Structure

express-server/
└── index.js

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✅ Step 1: Create a New Folder

mkdir express-server
cd express-server

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✅ Step 2: Initialize Project & Install Express

npm init -y
npm install express

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✅ Step 3: Create index.js File

echo. > index.js

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🧾 Full Code with Explanation

// index.js

const express = require("express");       // Import express
const app = express();                    // Create app instance
const port = 5000;                        // Port where server will run

// Middleware to handle JSON (important for POST, PUT later)
app.use(express.json());

// Home route
app.get("/", (req, res) => {
  res.send("Welcome to our Home Page!");
});

// Products route
app.get("/products", (req, res) => {
  const products = [
    { id: 1, name: "Mobile", price: 10000 },
    { id: 2, name: "Laptop", price: 45000 },
  ];
  res.json(products);
});

// About route
app.get("/about", (req, res) => {
  res.send("This is a demo Express API project.");
});

// Start the server
app.listen(port, () => {
  console.log(`🚀 Server is running at http://localhost:${port}`);
});

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▶️ How to Run

1. Open terminal

2. Navigate to your folder

3. Run:

node index.js

Now open your browser or Postman and visit:

• http://localhost:5000 → Home

• http://localhost:5000/products → Product list

• http://localhost:5000/about → About message

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🧠 What You Learned

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💡 Real-Life Use Case

Imagine you’re building the backend for a shopping website. These routes help you:

• Show homepage → /

• List all products → /products

• Company details → /about

Later, you’ll add more routes like:

• /products/:id

• /add-product

• /delete-product

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🔁 Code Flow Summary

Client (browser) → Server (Express) → Route matched → Response sent

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❓ FAQs – Beginner-Friendly Questions

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1. What is the purpose of express.json()?

It allows Express to understand JSON data from client (used in POST, PUT routes).

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2. Can we run this server on any port?

Yes! But make sure that port is not being used by another app (like React dev server).

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3. What happens if a route is not defined?

You’ll get a Cannot GET /something error.
To handle this, we can add a 404 route later like:

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

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4. Is Express still maintained and modern?

✅ Yes. Express is stable, maintained, and widely used in production (including MERN stack apps).

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🏁 Practice Task for Students

1. Add one more route: /contact → return contact email

2. Add a new route: /products/:id → return product by ID (static for now)

3. Use Postman to test /products route

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✅ Final Summary

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