Node.js

• Node.js is an open source server environment
• Node.js uses JavaScript on the server
• Node.js runs single-threaded, non-blocking, asynchronous programming
• Node.js can
  • Generate dynamic page content
  • Create, open, read, write, delete, and close files on the server
  • Collect form data
  • Add, delete, modify data in database
• npm is the standard package manager for Node.js

Basic commands

> node --version
> node file.js

> npm install <package-name><@version> <--save-dev>
> npm i <package-name>@latest <-D>

> npm update <package-name>
> npm start
> npm run <task-name>
> npm run start-dev

{
  "scripts": {
    "start-dev": "node lib/server-development",
    "start": "node lib/server-production"
  }
}

Modules

// myFirstModule.js
exports.myDateTime = function () {
  return Date();
};
// { myDateTime: func }

// other file
const dt = require("./myFirstModule");
console.log(dt.myDateTime());

Built-in modules

Modules	For
assert	test
buffer	binary data
child_processes	run a child processes
cluster	split single Node process -> multiple
crypto	handle OpenSSL cryptographic func
dns	DNS lookups & name resolution func
events	assign and trigger events
fs	handle file system
http	Node.js act as an HTTP server
https	Node.js act as an HTTPS server
net	create servers & clients
os	Provides information about operation system
path	handle file path
querystring	handle URL query string
readline	readable streams one line at the time
stream	handle streaming data
string_decoder	decode buffer objects to strings
timers	To execute a function after a given number of milliseconds
tls	implementing TLS (Transport Layer Security) and SSL (Secure Socket Layer)
url	parse URL strings
util	utility functions
vm	compile js code in a virtual machine - like eval() in js
zlib	compress or decompress files

HTTP

var http = require("http");
var url = require("url");

http
  .createServer(function (req, res) {
    res.writeHead(200, { "Content-Type": "text/html" });
    var q = url.parse(req.url, true).query;
    var txt = q.year + " " + q.month;
    res.end(txt); // Add to body
  })
  .listen(8080);

// http://localhost:8080/?year=2017&month=July -> "2017 July"

Testing

import assert from "node:assert";
import test from "node:test";

test("that 1 is equal 1", () => {
  assert.strictEqual(1, 1);
});
test("that throws as 1 is not equal 2", () => {
  // throws an exception because 1 != 2
  assert.strictEqual(1, 2);
});

Read & Hash a file

import { createHash } from "node:crypto";
import { readFile } from "node:fs/promises";

const hasher = createHash("sha1");
hasher.setEncoding("hex");
// ensure you have a `package.json` file for this test!
hasher.write(await readFile("package.json"));
hasher.end();
const fileHash = hasher.read();

Stream pipeline

import { pipeline } from "node:stream/promises";
import { createReadStream, createWriteStream } from "node:fs";
import { createGzip } from "node:zlib";

// ensure you have a `package.json` file for this test!
await pipeline(
  // 🤔
  createReadStream("package.json"),
  createGzip(),
  createWriteStream("package.json.gz")
);

Threads

import {
  Worker,
  isMainThread,
  workerData,
  parentPort,
} from "node:worker_threads";

if (isMainThread) {
  const data = "some data";
  const worker = new Worker(import.meta.filename, { workerData: data });
  worker.on("message", (msg) => console.log("Reply from Thread:", msg));
} else {
  const source = workerData;
  parentPort.postMessage(btoa(source.toUpperCase()));
}

How to keep packages up-to-date

Install npm-check-updates

npm install -g npm-check-updates

Scan packages (You can repeat this step)

ncu -u

Update packages (use npm or yarn)

npm install

When to use Module, CommonJS, Class

• Use ES Modules (import/export) for modern projects, especially if targeting both browser and Node.js environments, or if you want to use the latest JavaScript features.
• Use CommonJS (require/module.exports) for backward compatibility or if working with older Node.js projects and libraries.
• Use classes in JavaScript when:
  • You need to encapsulate data and behavior together (OOP).
  • You are building complex, reusable objects with inheritance or polymorphism.
  • In frameworks like React, where class components are used (though functional components are now more common).

For simpler tasks or functional programming, avoid classes and opt for regular functions or objects.

Resources

1. Node.js Documents (20.x)
2. w3schools - Node.js