Module5-NodeJS-TEST

Node.js is a JavaScript runtime built on Chrome's V8 engine that allows JavaScript to run on the server. Frameworks such as Express run on top of Node.js.

Node.js is especially useful for real-time, high-concurrency applications due to its non-blocking, event-driven execution model.

Non-Blocking I/O

Node.js uses a non-blocking execution model. Instead of waiting for operations (like database queries or file reads) to complete, Node continues executing other work and runs a callback or Promise when the operation finishes.

Blocking example (conceptual):

var data = database.query("select * from news");
print(data[0].title);

Non-blocking example:

database.query("select * from news", function(data){
	print(data[0].title);
});

Modern Node.js commonly uses async/await instead of callbacks:

const data = await database.query("select * from news");
console.log(data[0].title);

Installing Node.js

We use nvm (Node Version Manager) to install Node:

$ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.1/install.sh | bash
$ source ~/.bashrc
$ nvm install --lts
$ node -v
$ npm -v

Your First Node.js Application

Create a file named hello.js:

import http from "node:http";

http.createServer((req, res) => {
	res.writeHead(200, { "Content-Type": "text/plain" });
	res.end("Hello World\n");
}).listen(3456);

console.log("Server running at http://localhost:3456/");

Run:

$ node hello.js

Important: Modern Node uses ES Modules. Add this to package.json:

{
  "type": "module"
}

Installing Packages with npm

Install dependencies locally:

$ npm install mime

npm automatically records dependencies in package.json.

Static File Server

The following server serves static files from a directory:

import http from "node:http";
import { readFile } from "node:fs/promises";
import { existsSync } from "node:fs";
import path from "node:path";
import mime from "mime";
import { fileURLToPath } from "node:url";

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

const STATIC_DIR = "<STATIC DIRECTORY NAME>";

const app = http.createServer(async (req, resp) => {
	try {
		const urlPath = new URL(req.url, "http://localhost").pathname;
		const filename = path.join(__dirname, STATIC_DIR, decodeURIComponent(urlPath));

		if (!existsSync(filename)) {
			resp.writeHead(404, { "Content-Type": "text/plain" });
			resp.end("File not found");
			return;
		}

		const data = await readFile(filename);
		const mimetype = mime.getType(filename) || "application/octet-stream";

		resp.writeHead(200, { "Content-Type": mimetype });
		resp.end(data);
	} catch {
		resp.writeHead(500);
		resp.end("Server error");
	}
});

app.listen(3456);

Security Note: Production servers must validate file paths to prevent directory traversal attacks.

Opening Port 3456 on EC2

Follow the same process used previously to open port 80, but create a rule for TCP port 3456.

Node.js Security

Common risks include:

• XSS
• CSRF
• Injection attacks
• Unsafe use of eval()
• Directory traversal

Always validate inputs and sanitize outputs.

Node.js Conventions

Initialize a project:

$ npm init -y

Install dependencies:

$ npm install

package.json stores metadata and dependencies.