What is the difference between Node.js and browser-side JavaScript?

Both run JavaScript on the V8 engine, but they operate in completely different environments with different APIs and purposes.

1. Environment

• Browser — runs in a sandboxed browser tab, for client-side UI.

• Node.js — runs on the server or local machine, for backend and system-level tasks.

2. Global object

• Browser — window (and document, navigator).

• Node.js — global (and process, Buffer).

3. APIs available

• Browser — DOM, fetch, localStorage, alert, Web APIs.

• Node.js — fs, http, crypto, os, child_process, stream — no DOM.

4. Module system

• Browser — ES Modules (import/export) natively.

• Node.js — supports both CommonJS (require) and ES Modules.

5. Security model

1. Browser — sandboxed, restricted (same-origin policy, no file system access).

2. Node.js — full access to the OS, filesystem, and network.