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Node.js

What is Node.js?

Node.js is a powerful and versatile open-source runtime environment for executing JavaScript code on the server side. It enables developers to build scalable network applications with ease.

Key Features of Node.js

Open Source: Node.js is free to use and open-source, with a vibrant community of contributors.
Cross-Platform: Node.js runs on various operating systems including Windows, Linux, Unix, and macOS.
JavaScript Runtime: Node.js uses JavaScript, allowing developers to use the same language for both client-side and server-side development.
Asynchronous and Event-Driven: Node.js uses a non-blocking, event-driven architecture to handle concurrent operations efficiently.
Built on V8 Engine: Node.js is built on Chrome’s V8 JavaScript engine, which compiles JavaScript directly to native machine code for high performance.

Core Concepts

1. Asynchronous Programming

Node.js utilizes an asynchronous, non-blocking I/O model, which helps in building highly scalable applications.

const fs = require("fs");

// Non-blocking asynchronous read
fs.readFile("example.txt", "utf8", (err, data) => {
  if (err) throw err;
  console.log(data);
});

console.log("This will log before the file content.");

2. Event Loop

The event loop is a core feature of Node.js that manages and dispatches events or messages. It allows Node.js to perform non-blocking operations.

const EventEmitter = require("events");
const myEmitter = new EventEmitter();

myEmitter.on("event", () => {
  console.log("An event occurred!");
});

myEmitter.emit("event");

3. NPM (Node Package Manager)

NPM is the default package manager for Node.js, which hosts thousands of libraries and tools for Node.js development.

Install a package:
```
npm install <package-name>
```
Install a package globally:
```
npm install -g <package-name>
```
Uninstall a package:
```
npm uninstall <package-name>
```
Update packages:
```
npm update
```

4. Modules

Node.js uses modules to organize code into reusable components. There are built-in modules, third-party modules, and custom modules.

Built-in Module Example:

const http = require("http");

http
  .createServer((req, res) => {
    res.writeHead(200, { "Content-Type": "text/plain" });
    res.end("Hello World\n");
  })
  .listen(8080);

Custom Module Example:

math.js:

module.exports.add = (a, b) => a + b;

app.js:

const math = require("./math");
console.log(math.add(2, 3)); // 5

Getting Started with Node.js

1. Install Node.js

Download and install Node.js from the official website. The installation includes NPM.

2. Verify Installation

Check the installed versions of Node.js and NPM:

node -v
npm -v

3. Create Your First Node.js Application

Create a file named app.js with the following content:

console.log("Hello, Node.js!");

Run the application:

node app.js

4. Create a Simple Web Server

Create a file named server.js with the following content:

const http = require("http");

const hostname = "127.0.0.1";
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader("Content-Type", "text/plain");
  res.end("Hello World\n");
});

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

Run the server:

node server.js

Visit http://127.0.0.1:3000/ in your web browser to see “Hello World”.

Advanced Topics

1. Express.js

Express.js is a popular web framework for Node.js, designed for building web applications and APIs.

Install Express:
```
npm install express
```

Basic Express App:

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

app.get("/", (req, res) => {
  res.send("Hello World!");
});

app.listen(3000, () => {
  console.log("App is listening on port 3000!");
});

2. Asynchronous Programming with Promises and Async/Await

Promises and async/await are modern JavaScript features for handling asynchronous operations.

Promise Example:

const fs = require("fs").promises;

fs.readFile("example.txt", "utf8")
  .then((data) => console.log(data))
  .catch((err) => console.error(err));

Async/Await Example:

const fs = require("fs").promises;

async function readFile() {
  try {
    const data = await fs.readFile("example.txt", "utf8");
    console.log(data);
  } catch (err) {
    console.error(err);
  }
}

readFile();

Resources

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