3.1 — Quick Revision: Starting with Node.js

A compact cheat sheet covering Node.js fundamentals, setup, globals, npm, and package.json.

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< Interview Questions | README

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How to use this material

1. Read through once after completing all subtopics (3.1.a through 3.1.e).
2. Cover the right column of each table and try to recall the answer from the left column.
3. Print this page for quick reference before interviews or exams.
4. Flag anything you cannot recall and revisit that specific lesson file.

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Core Vocabulary

Term	Definition
Node.js	JavaScript runtime built on V8 + libuv + Node APIs — runs JS outside the browser
V8	Google's C++ JavaScript engine — compiles JS to machine code via JIT
libuv	C library providing the event loop, thread pool (4 default), and async I/O
Event loop	Single-threaded loop that delegates I/O and processes callbacks from queues
Non-blocking I/O	I/O operations are delegated and do not block code execution
npm	Node Package Manager — registry (2M+ packages) + CLI tool + website
npx	Run packages without global installation — always uses latest version
SemVer	MAJOR.MINOR.PATCH versioning — ^ allows minor+patch, ~ allows patch only
LTS	Long-Term Support — even-numbered Node.js versions (18, 20, 22)
REPL	Read-Eval-Print-Loop — interactive Node.js shell (node with no args)
CommonJS	require() / module.exports — Node.js original module system
ES Modules	import / export — the modern JavaScript standard

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Node.js vs Browser JavaScript

Feature	Browser	Node.js
Global object	window	global
Universal global	globalThis	globalThis
DOM	document, window.document	Not available
File system	Not available	fs module
HTTP server	Not available	http module
Module system	ES Modules	CommonJS + ES Modules
Process control	Not available	process object
__dirname	Not available	Available (CJS only)

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npm Commands Cheat Sheet

Command	What It Does
npm init -y	Create package.json with defaults
npm install / npm i	Install all dependencies from package.json
npm i express	Install package (adds to dependencies)
npm i nodemon -D	Install as devDependency
npm i -g typescript	Install globally
npm i express -E	Install exact version (no ^ or ~)
npm uninstall express	Remove a package
npm update	Update packages within SemVer range
npm outdated	Show which packages have newer versions
npm ls --depth=0	List top-level installed packages
npm audit	Check for security vulnerabilities
npm audit fix	Auto-fix vulnerabilities
npm ci	Clean install from lock file (for CI/CD)
npm run <script>	Run a custom script from package.json
npm start	Run the "start" script (no "run" needed)
npm test / npm t	Run the "test" script (no "run" needed)
npx <package>	Run a package without installing globally

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nvm Commands Cheat Sheet

Command	What It Does
nvm install --lts	Install latest LTS version
nvm install 20	Install latest Node.js 20.x
nvm use 20	Switch to Node.js 20.x
nvm ls	List installed versions
nvm alias default 20	Set default for new terminals
nvm current	Show active version
nvm uninstall 16	Remove a version
nvm use	Use version from .nvmrc

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node Command Cheat Sheet

Command	What It Does
node app.js	Run a JavaScript file
node	Start the REPL
node -v	Print Node.js version
node -e "code"	Execute inline code
node -p "expr"	Evaluate and print result
node --check app.js	Syntax check without running
node --watch app.js	Auto-restart on file changes (Node 18+)
node --env-file=.env app.js	Load .env file (Node 20.6+)

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package.json Key Fields

Field	Purpose	Example
name	Package name (lowercase, no spaces)	"my-api"
version	SemVer version	"1.0.0"
description	One-line summary	"REST API for my app"
main	Entry point for require()	"src/index.js"
type	Module system	"module" or "commonjs"
scripts	Custom npm commands	{ "start": "node server.js" }
dependencies	Runtime packages	{ "express": "^4.18.2" }
devDependencies	Development-only packages	{ "jest": "^29.7.0" }
peerDependencies	Consumer must provide	{ "express": "^4.0.0" }
engines	Required Node/npm version	{ "node": ">=20" }
private	Prevent accidental publishing	true
exports	Modern entry point map	{ ".": { "import": "..." } }

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Node.js Global Objects and Variables

Global	What It Is
process	Current process info — argv, env, cwd(), exit(), pid
console	Output methods — log, error, warn, table, time
__dirname	Absolute path to the directory of the current file (CJS only)
__filename	Absolute path to the current file (CJS only)
global	The global namespace object
globalThis	Universal global (works in browser and Node.js)
Buffer	Handle binary data
setTimeout	Schedule a callback after a delay
setInterval	Schedule a recurring callback
setImmediate	Schedule a callback in the check phase
require()	Import a module (CJS only)
module	Reference to the current module (CJS only)

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Dependency Types Quick Reference

Type	In production?	Install command	Example packages
dependencies	Yes	npm i express	express, mongoose, bcrypt, cors
devDependencies	No	npm i jest -D	jest, eslint, nodemon, prettier
peerDependencies	Must exist	Consumer installs	express (for plugins)

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SemVer Range Symbols

Symbol	Meaning	^4.18.2 allows
^ (caret)	Minor + patch updates	>=4.18.2 <5.0.0
~ (tilde)	Patch updates only	>=4.18.2 <4.19.0
(none)	Exact version	Only 4.18.2
*	Any version	Latest

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CommonJS vs ES Modules

Feature	CommonJS	ES Modules
Import	require('pkg')	import pkg from 'pkg'
Export	module.exports = ...	export default ...
Loading	Synchronous	Asynchronous
Top-level await	No	Yes
Tree-shaking	No	Yes
__dirname	Available	Use import.meta.url
File extension	.js or .cjs	.js (with "type":"module") or .mjs
Default in Node.js	Yes	Opt-in via "type":"module"

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Event Loop Phases (Simplified)

┌─► timers         ← setTimeout, setInterval callbacks
│   pending        ← deferred I/O callbacks
│   poll           ← retrieve + execute I/O callbacks
│   check          ← setImmediate callbacks
│   close          ← socket.on('close') callbacks
└───────────────── (repeat)

Microtasks (process.nextTick, Promises) run BETWEEN every phase.

Execution order:

1. Synchronous code
2. process.nextTick callbacks
3. Resolved Promise callbacks (.then)
4. setTimeout / setImmediate callbacks

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Master Workflow: New Project Setup

# 1. Create and enter project directory
mkdir my-project && cd my-project

# 2. Set Node.js version
echo "20" > .nvmrc && nvm use

# 3. Initialize project
npm init -y

# 4. Set up .gitignore
echo "node_modules/\n.env\n.DS_Store\ndist/\ncoverage/" > .gitignore

# 5. Create entry point
touch index.js

# 6. Install dependencies
npm i express dotenv cors
npm i -D nodemon jest eslint

# 7. Initialize git
git init && git add -A && git commit -m "Initial commit"

# 8. Run
npm start        # production
npm run dev      # development

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Files to Commit vs Ignore

Commit	Ignore (.gitignore)
package.json	node_modules/
package-lock.json	.env
.nvmrc	.DS_Store
.gitignore	dist/
Source code (src/)	coverage/

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