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JavaScript

47 cheat sheets

JavaScript#

A practical reference for JavaScript in Node.js and the browser — from running your first script to configuring a production-grade toolchain.

What’s in this section#

TopicPages
Runtimeinstallation · node-runtime
Package managersnpm · npx · pnpm · yarn
Project configpackage-json · modules
Asyncasync-await · promises · fetch
Languagearray-methods · regex · errors
Toolingeslint · prettier · vitest · vite
  1. Installation — install Node.js via nvm or the official installer
  2. Node runtime — the REPL, running scripts, environment variables
  3. npm — the default package manager; understand it before the alternatives
  4. package.json — the heart of every JavaScript project
  5. modules — CommonJS vs ESM; when to use each
  6. async-await and promises — the async model
  7. fetch — HTTP requests in modern JS and Node
  8. array-methods — map, filter, reduce, and friends
  9. eslint + prettier — linting and formatting
  10. vitest + vite — testing and bundling

[!TIP] If you are working in TypeScript rather than plain JavaScript, start with the TypeScript section after completing the Node and npm pages here.

Node.js Installation

Install Node.js on Windows, macOS, and Linux using winget, Homebrew, apt, nvm, Volta, or fnm. Covers version managers, LTS vs current, and verifying your install.

Apr 26, 2026
javascript node installation nvm volta fnm

Node.js Runtime

How to use the Node.js runtime — REPL, running scripts, CLI flags, ESM vs CJS modules, built-in node: modules, the process object, and modern globals like fetch and structuredClone.

Apr 26, 2026
javascript node runtime cli esm cjs modules

npm Package Manager

Complete npm reference — installing packages, scripts, workspaces, package.json anatomy, audit, publish, link, lockfiles, and registry configuration.

Apr 26, 2026
javascript npm packages cli node

npx — Execute npm Packages

Run npm package binaries without global installs using npx. Covers resolution order, version pinning, --yes, --no-install, npm exec, scaffolders, and cache management.

Apr 26, 2026
javascript npx npm cli node

node:fs — File System

Node.js file system module — the three APIs (callback, sync, promises), reading and writing files, directory operations, watchers, atomic writes, and path module pairing.

May 25, 2026
javascript node filesystem fs language

node:stream — Streams

Node.js streams — Readable, Writable, Duplex, and Transform, the modern pipeline() API, backpressure, async iterators, Web Streams interop, and patterns for piping files, HTTP bodies, and gzip compression.

May 25, 2026
javascript node streams pipeline language

Fastify — Node Web Framework

Fastify is a high-performance Node.js web framework with schema-driven validation, plugin encapsulation, hooks, decorators, and built-in Pino logging — covering routes, plugins, hooks, error handling, and production hardening.

May 25, 2026
javascript node backend framework fastify web

pnpm Package Manager

Fast, disk-efficient package manager using a content-addressable store and hard-links. Covers install, add, remove, scripts, dlx, exec, the pnpm store, and workspaces.

Apr 26, 2026
javascript pnpm packages cli node

Yarn Package Manager

Yarn is a fast, deterministic package manager from Meta. Covers Yarn Classic (v1) vs Yarn Berry (v4), install, add, remove, workspaces, Plug'n'Play, and migration tips.

Apr 26, 2026
javascript yarn packages cli node

package.json Reference

Complete reference for the Node.js package manifest — name, version, scripts, dependencies, exports, workspaces, and the packageManager field for Corepack.

Apr 26, 2026
javascript npm packages node json

JavaScript Modules

CommonJS vs ES Modules in Node.js — syntax, how Node chooses the module system, dynamic import, top-level await, CJS/ESM interop, and common pitfalls.

Apr 26, 2026
javascript modules esm commonjs node

Array Methods

JavaScript arrays have ~30 built-in methods for transforming, searching, and reducing data. Covers mutation, non-mutation, search, boolean, iteration, and static methods with real examples.

Apr 26, 2026
javascript arrays language

Async / Await

async/await syntax, error handling, parallel execution with Promise.all, sequential vs parallel loops, top-level await, AbortController, and common mistakes.

Apr 26, 2026
javascript async promises language

Regular Expressions

JavaScript has built-in RegExp support (ES2018+ with named groups, lookbehind, dotAll). Covers literal syntax, flags, character classes, methods, named captures, and common patterns.

Apr 26, 2026
javascript regex language

Promises

JavaScript Promises represent the eventual completion or failure of an async operation. Covers states, chaining, combinators, callback conversion, AbortController, and common anti-patterns.

Apr 26, 2026
javascript promises async language

Fetch API

The browser and Node 18+ built-in HTTP client that returns Promises. Covers GET/POST/PUT/DELETE, headers, error handling, streaming, AbortController, uploads, credentials, and CORS.

Apr 26, 2026
javascript fetch http api language

Error Handling

JavaScript error handling with try/catch/finally, built-in error types, custom error classes, error chaining with cause (ES2022), async errors, and practical patterns like result objects.

Apr 26, 2026
javascript errors language

Bun — All-in-One JavaScript Runtime & Toolkit

Bun is a fast all-in-one JavaScript runtime, package manager, bundler, and test runner written in Zig — a drop-in replacement for Node.js and npm with built-in TypeScript and JSX support.

May 25, 2026
javascript runtime bun cli typescript tooling

diff2html-cli — Beautiful HTML Diffs from the Terminal

Convert unified diffs and git diff output into styled HTML side-by-side or line-by-line diff views from the command line.

May 4, 2026
diff html cli tooling

wrangler — Cloudflare Workers CLI

Cloudflare's official CLI for building, configuring, and deploying Workers, Pages, KV, R2, D1, Vectorize, Hyperdrive, Queues, Workflows, and Secrets.

May 24, 2026
wrangler cloudflare workers cli deploy edge

Deno — Secure JavaScript & TypeScript Runtime

Deno is a secure, modern JavaScript and TypeScript runtime built on V8 with permission-based sandboxing, built-in TypeScript, a curated standard library on JSR, and a complete toolchain (fmt, lint, test, bench, compile).

May 25, 2026
javascript runtime deno typescript cli tooling

Astro — Content-First Web Framework

Astro is a multi-page, content-first web framework with an islands architecture — server-render Markdown, MDX, and component pages to static HTML, then hydrate interactive widgets selectively with React, Vue, Svelte, or Solid.

May 25, 2026
javascript framework astro ssg web content

vercel — Vercel frontend cloud CLI

Vercel's official CLI for deploying frontend apps, managing environments, syncing env vars, tailing logs, and rolling back via alias re-pointing.

May 31, 2026
vercel deploy edge cli nextjs tooling

ESLint

The standard JavaScript/TypeScript linter. Covers flat config (v9), legacy .eslintrc, running, rules, plugins, TypeScript integration, VS Code, and pre-commit hooks.

Apr 26, 2026
javascript eslint linting tooling

ncu — npm-check-updates CLI for dependency upgrades

The ncu CLI from npm-check-updates rewrites package.json to bump dependency versions — interactive mode, filters, doctor rollback, and workspaces support.

May 31, 2026
ncu npm upgrade dependencies cli tooling

Prettier

Opinionated code formatter for JS/TS/CSS/HTML/JSON/Markdown. Covers config options, .prettierignore, VS Code integration, ESLint compatibility, lint-staged, and CI usage.

Apr 26, 2026
javascript prettier formatting tooling

Biome — One toolchain for lint, format, and import sorting

Rust-based all-in-one linter and formatter for JS/TS/JSON/CSS/GraphQL. Single binary, single config, 10-100x faster than ESLint+Prettier.

May 25, 2026
javascript biome linting formatting tooling

Vite

Next-generation frontend build tool using native ES modules for near-instant dev server startup and Rollup for production bundles. Covers setup, config, HMR, env vars, assets, CSS, and plugins.

Apr 26, 2026
javascript vite build bundler tooling

Vitest

Vite-native unit test framework with a Jest-compatible API. Covers setup, writing tests, matchers, mocking, timers, async testing, coverage, and UI mode.

Apr 26, 2026
javascript vitest testing tooling

vue (@vue/cli) — Legacy Vue project scaffolder

The legacy @vue/cli command-line tool for scaffolding and serving Vue projects — deprecated in favour of create-vue + Vite, retained as reference for existing apps.

May 31, 2026
vue vue-cli scaffolding deprecated cli tooling

Playwright — End-to-end browser testing across Chromium, Firefox, WebKit

Cross-browser end-to-end test runner from Microsoft with auto-waiting, role-based selectors, trace viewer, and codegen.

May 25, 2026
javascript playwright testing browser e2e

Zod — TypeScript-first schema validation with static type inference

TypeScript-first runtime validation library. Define schemas, validate inputs, infer static types — works at API boundaries, env config, forms, and tRPC.

May 25, 2026
javascript typescript zod validation schema

React Basics — Function components, hooks, and JSX

Foundational React patterns — function components, JSX, props, hooks (useState, useEffect, useRef, useContext), list rendering, and form handling — with TypeScript throughout.

May 25, 2026
javascript react ui framework typescript

Day.js — Tiny, immutable date library

Parse, format, manipulate, compare, and convert timezones for dates in JavaScript using Day.js — a 2 kB Moment-compatible alternative with a plugin-based architecture.

May 25, 2026
javascript dates time library tooling

Chalk — Terminal string styling for Node

Apply ANSI colours, backgrounds, and text styles to terminal output in Node.js using Chalk's chainable API, plus comparisons with picocolors and patterns for building polished CLI UX.

May 25, 2026
javascript node cli terminal library

dotenv — Environment Variables from .env Files

Load configuration and secrets from .env files into process.env at startup, with multi-environment files, variable expansion, schema validation, and Node 20.6+ built-in --env-file alternatives.

May 25, 2026
javascript node config env dotenv

Prisma — Type-Safe Node.js ORM

Schema-first ORM for Node.js with auto-generated typed client, declarative migrations, relations, transactions, and seeding — for PostgreSQL, MySQL, SQLite, MongoDB, and more.

May 25, 2026
javascript typescript orm database prisma node

Commander.js — Node.js Command-Line Interfaces

Build full-featured Node.js CLIs with positional arguments, typed options, subcommands, auto-generated help, lifecycle hooks, and a distributable bin in package.json.

May 25, 2026
javascript node cli commander tooling

Cypress — CLI and configuration

Day-to-day Cypress CLI commands and config patterns — interactive runs, headless CI, intercepts, sessions, component testing, and Playwright comparison.

May 31, 2026
cypress cli testing e2e

esbuild — CLI & transform API

Daily-driver reference for esbuild — bundle CLI, transform API, JS API patterns, common build recipes.

May 31, 2026
esbuild cli bundler build tooling

Jest — CLI and configuration

Day-to-day Jest CLI commands and config patterns — running tests, mocks, snapshots, coverage, watch mode, and migration tips.

May 31, 2026
jest cli testing tooling

nodemon — Auto-restart on file change CLI

Daily-driver reference for nodemon — watch flags, exec patterns, config files, lifecycle events.

May 31, 2026
nodemon cli dev-tool watcher

rollup — CLI & plugin patterns

Daily-driver reference for rollup — CLI commands, multi-format output, plugin chain patterns, library publishing config.

May 31, 2026
rollup cli bundler build tooling

ts-node — Run TypeScript in Node CLI

Daily-driver reference for the ts-node CLI — REPL, transpile-only mode, ESM loader, common script patterns.

May 31, 2026
ts-node cli typescript runner

tsx — TypeScript Execute CLI

Daily-driver reference for the tsx CLI — run TS files, watch mode, ESM/CJS handling, Node loader integration.

May 31, 2026
tsx cli typescript runner dev-tool

Turborepo (turbo) — CLI and pipeline configuration

Day-to-day Turborepo CLI commands and turbo.json config patterns — pipelines, filters, remote cache, prune, and CI integration.

May 31, 2026
turbo cli monorepo build

webpack — CLI & config patterns

Daily-driver reference for webpack — CLI commands, dev server, loaders, plugins, code splitting, common config recipes.

May 31, 2026
webpack cli bundler build tooling