Environment Variables in Node.js

What are Environment Variables?

Environment variables are dynamic values that affect the behavior of running processes. They’re used to store configuration settings, API keys, and other sensitive data.

Accessing Environment Variables

// Access via process.env
const port = process.env.PORT || 3000;
const dbUrl = process.env.DATABASE_URL;
const apiKey = process.env.API_KEY;

console.log(process.env.NODE_ENV); // development, production, test

Setting Environment Variables

Command Line

# Linux/Mac
PORT=3000 node app.js
NODE_ENV=production node app.js

# Windows
set PORT=3000 && node app.js

.env File

# .env
PORT=3000
DATABASE_URL=mongodb://localhost:27017/mydb
API_KEY=your-api-key-here
NODE_ENV=development

Using dotenv Package

// Install: npm install dotenv
require('dotenv').config();

const port = process.env.PORT;
const dbUrl = process.env.DATABASE_URL;

Configuration Example

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

module.exports = {
  port: process.env.PORT || 3000,
  database: {
    url: process.env.DATABASE_URL,
    name: process.env.DB_NAME
  },
  jwt: {
    secret: process.env.JWT_SECRET,
    expiresIn: process.env.JWT_EXPIRES_IN || '1h'
  },
  email: {
    host: process.env.EMAIL_HOST,
    port: process.env.EMAIL_PORT,
    user: process.env.EMAIL_USER,
    pass: process.env.EMAIL_PASS
  }
};

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

app.listen(config.port, () => {
  console.log(`Server running on port ${config.port}`);
});

Environment-Specific Configuration

const env = process.env.NODE_ENV || 'development';

const config = {
  development: {
    port: 3000,
    database: 'mongodb://localhost:27017/dev'
  },
  production: {
    port: process.env.PORT,
    database: process.env.DATABASE_URL
  },
  test: {
    port: 3001,
    database: 'mongodb://localhost:27017/test'
  }
};

module.exports = config[env];

Best Practices

1. Never Commit .env Files

# .gitignore
.env
.env.local
.env.*.local

2. Provide .env.example

# .env.example
PORT=3000
DATABASE_URL=your_database_url
API_KEY=your_api_key
JWT_SECRET=your_jwt_secret

3. Validate Environment Variables

const requiredEnvVars = [
  'DATABASE_URL',
  'JWT_SECRET',
  'API_KEY'
];

requiredEnvVars.forEach(varName => {
  if (!process.env[varName]) {
    throw new Error(`Missing required environment variable: ${varName}`);
  }
});

4. Use Type Conversion

const port = parseInt(process.env.PORT, 10);
const enableCache = process.env.ENABLE_CACHE === 'true';
const maxConnections = Number(process.env.MAX_CONNECTIONS);

Cross-Platform Support

// Use cross-env for cross-platform compatibility
// Install: npm install --save-dev cross-env

// package.json
{
  "scripts": {
    "start": "cross-env NODE_ENV=production node app.js",
    "dev": "cross-env NODE_ENV=development nodemon app.js"
  }
}

Interview Tips

• Explain purpose: Configuration and secrets management
• Show access: process.env object
• Demonstrate dotenv: Loading from .env files
• Discuss security: Never commit sensitive data
• Mention validation: Check required variables

Summary

Environment variables configure applications without changing code. Access via process.env. Use dotenv package to load from .env files. Never commit .env files to version control. Validate required variables on startup.