Environment Variables in Node.js

Environment variables store configuration outside your code. Essential for secrets.

Why Environment Variables?

```javascript // ❌ Never do this const apiKey = 'sk-secret-key-12345';

// ✅ Use environment variables const apiKey = process.env.API_KEY; ```

Accessing Environment Variables

```javascript // Access any env variable console.log(process.env.PATH); console.log(process.env.HOME); console.log(process.env.NODE_ENV); // 'development' or 'production' ```

Setting Variables (Command Line)

```bash # Single command PORT=3000 node app.js

Multiple variables PORT=3000 NODE_ENV=production node app.js

Windows (PowerShell) $env:PORT=3000; node app.js ```

Using dotenv Package

Install: ```bash npm install dotenv ```

Create `.env` file: ``` # .env PORT=3000 DATABASE_URL=mongodb://localhost/mydb API_KEY=your-secret-key DEBUG=true ```

Load in your app: ```javascript // app.js - Load at the very top! require('dotenv').config();

console.log(process.env.PORT); // 3000 console.log(process.env.API_KEY); // your-secret-key ```

.env File Best Practices

``` # Use comments for documentation # Database Configuration DATABASE_URL=mongodb://localhost/mydb DATABASE_NAME=myapp

API Keys STRIPE_KEY=sk_test_... SENDGRID_KEY=SG....

Feature Flags ENABLE_CACHE=true DEBUG_MODE=false ```

Don't Commit .env!

Add to .gitignore: ``` # .gitignore .env .env.local .env.*.local ```

Create .env.example for documentation: ``` # .env.example (commit this) PORT=3000 DATABASE_URL=your_database_url_here API_KEY=your_api_key_here ```

Different Environments

```javascript // Load different files based on environment const envFile = process.env.NODE_ENV === 'production' ? '.env.production' : '.env';

require('dotenv').config({ path: envFile }); ```

Type Conversion

Environment variables are always strings: ```javascript // .env: PORT=3000

const port = process.env.PORT; // "3000" (string!) const port = parseInt(process.env.PORT, 10); // 3000 (number)

// Booleans const debug = process.env.DEBUG === 'true'; // boolean ```

Required Variables Check

```javascript const required = ['DATABASE_URL', 'API_KEY', 'JWT_SECRET'];

for (const key of required) { if (!process.env[key]) { console.error(`Missing required env variable: ${key}`); process.exit(1); } } ```

Config Module Pattern

```javascript // config.js require('dotenv').config();

module.exports = { port: parseInt(process.env.PORT, 10) || 3000, db: { url: process.env.DATABASE_URL, name: process.env.DATABASE_NAME || 'myapp' }, jwt: { secret: process.env.JWT_SECRET, expiresIn: '7d' }, isDev: process.env.NODE_ENV !== 'production' }; ```

```javascript // app.js const config = require('./config');

app.listen(config.port); ```

Key Takeaway

Use environment variables for all secrets and configuration. Install `dotenv`, create `.env` file, add it to `.gitignore`, and load with `require('dotenv').config()` at the top of your entry file. Create a config module for clean access.