Glossary

Quick definitions, A to Z. Each term is explained in depth in its guide; this is the reminder card.

• Arrow function — compact function syntax ((x) => x * 2). Inherits this; the default for callbacks.
• async/await — syntax for working with promises; await pauses your function until the promise settles.
• Callback — a function passed to another function, run later. Old async style; modern code prefers promises.
• CommonJS — the older module system (require/module.exports). You'll read it, rarely write it.
• const — declares a binding that can't be reassigned. The default choice.
• Destructuring — unpacking objects/arrays in one line (const { name } = user).
• ES modules — the modern module system (import/export). Use for new code.
• Event loop — Node's mechanism: one thread parks waiting functions and resumes them when I/O finishes.
• Falsy — values that count as false in if: false, 0, "", null, undefined, NaN.
• let — declares a reassignable variable.
• Module — a file sharing code via import/export.
• node_modules — where npm installs packages. A cache: never edit it, never commit it.
• npm — Node's package manager and registry; also runs project scripts.
• Nullish coalescing (??) — "use the right side if the left is null/undefined."
• Optional chaining (?.) — safely drills into nested data, yielding undefined instead of throwing.
• package.json — your project's ID card: name, version, dependencies, scripts.
• package-lock.json — pins exact dependency versions. Commit it.
• Promise — an IOU for a future value: pending, fulfilled, or rejected.
• REPL — the interactive node prompt for trying snippets.
• Template literal — backtick strings with ${} interpolation.
• Truthy — everything not falsy (including [] and {}).
• Unhandled rejection — a failed promise nobody handled; crashes the process by default.
• V8 — Google's JavaScript engine that powers Node (and Chrome).