> For the complete documentation index, see [llms.txt](https://www.anandisheladiya.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.anandisheladiya.com/skills-and-experience/backend/nodejs-and-expressjs.md). # NodeJS & ExpressJS ### **Introduction** **Node.js** is a powerful, event-driven, non-blocking JavaScript runtime that allows developers to build **scalable and high-performance backend applications**. It is built on **Google Chrome's V8 JavaScript engine**, making it **fast and efficient** for server-side development. **Express.js** is a lightweight and flexible **web framework for Node.js**, designed to simplify the process of building web applications and APIs. It provides essential features like **routing, middleware, and HTTP handling**, making backend development smoother. ### **Why Use Node.js?** * **Asynchronous & Non-blocking** – Handles multiple requests efficiently. * **High Performance** – Uses **V8 Engine**, which compiles JavaScript to machine code. * **Single Programming Language** – JavaScript can be used for both **frontend** & **backend**. * **Huge Ecosystem** – Over **1.5 million packages** available via **npm**. * **Microservices & Real-time Apps** – Ideal for **APIs, chat apps, and live streaming**. * **Scalability** – Perfect for handling thousands of concurrent users. ### **Why Use Express.js?** * **Minimal & Fast** – No unnecessary bloat; just the essentials. * **Easy Routing System** – Handles URLs efficiently. * **Middleware Support** – Customize requests and responses. * **Template Engines** – Supports **EJS, Pug, and Handlebars** for dynamic HTML. * **API Development** – Ideal for creating RESTful & GraphQL APIs. ## **Getting Started with Node.js & Express.js** ### **1️⃣ Install Node.js** Download and install Node.js from .\ Check the installation: ```bash node -v # Check Node.js version npm -v # Check npm version ``` ### **2️⃣ Initialize a New Project** Create a new project and set up `package.json`: ```bash mkdir myapp && cd myapp npm init -y ``` 3️⃣ Install Express.js ```bash npm install express ``` ## **Creating a Simple Express Server** **Create a `server.js` file and add the following:** ```javascript const express = require("express"); const app = express(); const PORT = 3000; app.get("/", (req, res) => { res.send("Hello, World! 🌍"); }); app.listen(PORT, () => { console.log(`🚀 Server is running at http://localhost:${PORT}`); }); ``` Run the server: ```bash node server.js ``` Now, open **** in your browser. ## **Express.js Routing** **Defining Different Routes** ```javascript app.get("/", (req, res) => { res.send("Home Page"); }); app.get("/about", (req, res) => { res.send("About Page"); }); app.post("/submit", (req, res) => { res.send("Data Submitted Successfully"); }); ``` Handling URL Parameters ```javascript app.get("/user/:name", (req, res) => { res.send(`Hello, ${req.params.name}!`); }); ``` **Visit:** `http://localhost:3000/user/John`\ **Output:** `"Hello, John!"`
## **Using Middleware in Express.js** Middleware functions allow you to **modify requests/responses** before they reach the final handler. **Example of Middleware** ```javascript app.use((req, res, next) => { console.log(`Incoming Request: ${req.method} ${req.url}`); next(); // Call the next middleware or route handler }); ``` **Built-in Middleware** ```javascript app.use(express.json()); // Parse JSON requests app.use(express.urlencoded({ extended: true })); // Parse form data ``` **Third-party Middleware (CORS, Morgan)** ```bash npm install cors morgan ``` ```javascript const cors = require("cors"); const morgan = require("morgan"); app.use(cors()); // Enables cross-origin requests app.use(morgan("dev")); // Logs requests in console ``` ## **Serving Static Files (HTML, CSS, Images, JS)** Express can serve **static files** from a directory like `public/`. ```javascript app.use(express.static("public")); ``` Place **HTML, CSS, JS, images** inside the `public/` folder, and access them directly in the browser. ## **Handling Forms & JSON Data** **Install Body Parser (Optional, built-in in Express 4.16+)** ```bash npm install body-parser ``` Parse Form Data & JSON Requests ```javascript const bodyParser = require("body-parser"); app.use(bodyParser.json()); app.use(bodyParser.urlencoded({ extended: true })); ``` Handling Form Submissions ```javascript app.post("/login", (req, res) => { const { username, password } = req.body; res.send(`Logged in as ${username}`); }); ``` ## **Connecting Express.js with a Database** ### **MongoDB (Using Mongoose)** **Install Mongoose** ```bash npm install mongoose ``` **Connect to MongoDB** ```javascript const mongoose = require("mongoose"); mongoose.connect("mongodb://localhost:27017/mydb", { useNewUrlParser: true, useUnifiedTopology: true, }); const UserSchema = new mongoose.Schema({ name: String, age: Number }); const User = mongoose.model("User", UserSchema); // Create a User app.post("/users", async (req, res) => { const user = new User(req.body); await user.save(); res.send("User saved!"); }); ``` ## **Building a REST API with Express.js** **Create a Simple API** ```javascript const products = [ { id: 1, name: "Laptop", price: 1000 }, { id: 2, name: "Phone", price: 500 }, ]; // Get all products app.get("/api/products", (req, res) => { res.json(products); }); // Get a single product by ID app.get("/api/products/:id", (req, res) => { const product = products.find((p) => p.id == req.params.id); product ? res.json(product) : res.status(404).send("Not found"); }); // Create a new product app.post("/api/products", (req, res) => { const newProduct = req.body; products.push(newProduct); res.status(201).json(newProduct); }); ``` ## **Real-time Apps with Socket.io** **Install Socket.io** ```bash npm install socket.io ``` **Simple WebSocket Chat App** ```javascript const http = require("http").createServer(app); const io = require("socket.io")(http); io.on("connection", (socket) => { console.log("User connected"); socket.on("message", (msg) => io.emit("message", msg)); }); http.listen(3000, () => console.log("Chat server running on port 3000")); ``` ## **Conclusion** Node.js & Express.js are **powerful tools** for building **scalable, fast, and efficient** backend applications. Whether you're creating **REST APIs, real-time apps, or full-stack projects**, they provide everything you need.