10. Express.js – Build Your First Web Application

Express.js – Build Your First Web Application

Express.js is a fast, minimal, and flexible Node.js framework used to build web applications and APIs easily. It simplifies server creation and routing compared to the basic HTTP module.

Client → Express Server → Response

1. What is Express.js?

Express.js is a backend framework built on top of Node.js that helps us:

• Create servers easily
• Handle routes
• Build APIs
• Manage requests and responses

Express.js removes complexity and makes Node.js development faster.

2. Installing Express.js

Run this command in your project folder:

npm init -y
npm install express

3. Creating Your First Express Server

const express = require("express");

const app = express();

app.get("/", (req, res) => {
  res.send("Hello from Express.js");
});

app.listen(3000, () => {
  console.log("Server running on port 3000");
});

Open browser: http://localhost:3000

4. Understanding the Code

• express() → Creates app
• app.get() → Handles route
• req → Request
• res → Response
• app.listen() → Starts server

5. Creating Multiple Routes

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

app.get("/about", (req, res) => {
  res.send("About Page");
});

app.get("/contact", (req, res) => {
  res.send("Contact Page");
});

6. Sending JSON Response

app.get("/api", (req, res) => {
  res.json({ name: "Node.js", type: "Backend" });
});

7. Real-World Usage

• Building REST APIs
• Handling user requests
• Backend for web apps
• Microservices

8. Common Beginner Mistakes

• Forgetting to install express
• Not restarting server
• Wrong route path

Always restart server after changes.

Conclusion

Now you can build your first Express.js server easily.

Next: Express Routing (GET, POST, PUT, DELETE)

Your Node.js journey just became real backend development 🚀