Node.js vs the browser

Node.jsJunior~2 min read

1. Where the code runs

Environment	Where it runs	Main purpose
Node.js	On a server or locally on a machine	Server logic, APIs, automation, utilities
Browser	On the client side (in the user's browser)	UI work, DOM, user interaction

Capability	Node.js	Browser
Filesystem access	Yes, `fs`	None
Network access (TCP, HTTP server)	Yes, `http`, `net`	Partial: only HTTP requests via `fetch`
DOM access (HTML, page elements)	None	Yes
Web APIs (`fetch`, `localStorage`, `WebSocket`)	Partial (Node 18+ added some)	Full access
Global objects	`global`, `process`, `__dirname`	`window`, `document`, `navigator`

Feature	Node.js	Browser
Module system	CommonJS (`require`) and ES Modules (`import`)	ES Modules only
Package manager	npm, pnpm, yarn	None (needs a bundler - Webpack, Vite, etc.)
Importing packages	Directly from `node_modules`	Via bundling into a single file

Both environments run the V8 engine, but Node.js wraps it with its own system APIs.
Node.js uses the event loop for asynchronous I/O: reading files, requests, processes.
In the browser, the event loop handles UI events: clicks, timers, requests to the server.

Aspect	Node.js	Browser
System access	Yes	None
Code isolation	None (code can access the disk and network)	Yes (sandbox)
Trust level	Server-side code	Untrusted environment (the user's browser)

Node.js:

javascript

// Working with files
const fs = require('fs');
fs.writeFileSync('text.txt', 'Hello from Node.js!');

Browser:

javascript

// Working with the DOM
document.body.innerHTML = '<h1>Hello from Browser!</h1>';

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