Node.js built-in globals and useful CLI flags

Globals You Get for Free

Node.js injects several globals into every module. Unlike browser globals, these are specific to the runtime environment.

console.log(__dirname);   // absolute path to current directory
console.log(__filename);  // absolute path to current file

// Use __dirname for reliable file paths:
const path = require('path');
const config = path.join(__dirname, 'config', 'app.json');

In ESM, __dirname is not available. Use import.meta.url instead:

import { fileURLToPath } from 'url';
import { dirname } from 'path';
const __dirname = dirname(fileURLToPath(import.meta.url));

Useful CLI Flags

--watch (Node 18+) restarts on file changes — no nodemon needed for basic dev work. --inspect opens the V8 debugger so Chrome DevTools can attach.

node --watch src/index.js
node --inspect src/index.js

Environment Variables

Load .env files natively from Node 20.6+ with --env-file:

node --env-file=.env src/index.js

Always add .env to .gitignore. Never commit secrets.