JavaScript Cheat Sheet

JavaScript cheat sheet with real commands and snippets for setup, core workflows, debugging, and production-safe automation patterns. If you are working across tools, pair this with the HTML Cheat Sheet and Firebase Cheat Sheet.

Setup and Tooling

Goal: Install and verify language toolchain

# Run node command
node --version

# Run npm command
npm --version

# Run npm command
npm init -y

Core Workflows

Goal: Run and build source code

# Execute node workflow
node src/index.js

# Execute node workflow
node --watch src/index.js

Goal: Use a practical code snippet

// Async function with structured error handling
async function fetchJson(url) {
  const res = await fetch(url);
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  return res.json();
}

Testing and Formatting

Goal: Run automated tests

# Execute test-related command
node --test

# Execute test-related command
npm test

Goal: Run lint and formatter checks

# Execute quality command
npx eslint .

# Execute quality command
npx prettier -w .

Automation and CI

Goal: Create a repeatable CI shell step

# Run strict shell mode for CI step
set -euo pipefail

# Install dependencies deterministically
npm ci || pip install -r requirements.txt || true

# Run tests and fail fast on errors
node --test

Debugging and Troubleshooting

Goal: Trace runtime issues

# Print runtime and package manager versions
node --version || python --version || true

# Search stack traces and TODO markers
rg "Traceback|Exception|TODO" .

# Re-run tests with verbose output
node --test -v || node --test --verbose || true

Common Gotchas

• Pin JavaScript language/runtime versions in local and CI environments.
• Keep formatting and linting automated to avoid noisy diffs in code review.
• Prefer explicit dependency lock files for reproducible builds.
• Write small, deterministic tests that can run quickly in pre-commit checks.
• Document compiler/interpreter flags used in production builds.

Related Sheets

• HTML Cheat Sheet — daily HTML commands and production-ready examples.
• Firebase Cheat Sheet — daily Firebase commands and production-ready examples.
• htmx Cheat Sheet — daily htmx commands and production-ready examples.