Environment Variables in Node.js

Environment variables are external values used to configure applications without changing source code.
They are commonly used to store sensitive information and environment-specific settings.

1. Why Environment Variables Are Important

• Keep secrets out of source code

• Support different environments (development, testing, production)

• Improve security

• Simplify configuration management

Examples:

• Database URLs

• API keys

• Port numbers

2. Accessing Environment Variables in Node.js

Node.js provides the process.env object.

console.log(process.env.PORT);

3. Setting Environment Variables

3.1 On Windows

set PORT=3000
node app.js

3.2 On macOS / Linux

export PORT=3000
node app.js

4. Using Environment Variables in Code

const port = process.env.PORT || 3000;

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

5. Using .env Files (dotenv Package)

Managing many environment variables manually is difficult.
The dotenv package loads variables from a .env file.

Install dotenv

npm install dotenv

Create .env File

PORT=4000
DB_URL=mongodb://localhost:27017/appdb

Load Environment Variables

require('dotenv').config();

6. Using Environment Variables with Express.js

const express = require('express');
require('dotenv').config();

const app = express();
const PORT = process.env.PORT;

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

7. Environment-Based Configuration

if (process.env.NODE_ENV === 'production') {
  // production settings
} else {
  // development settings
}

8. Security Best Practices

• Never commit .env files to Git

• Add .env to .gitignore

• Use strong secret values

• Rotate secrets regularly

9. Common Environment Variables

10. Common Mistakes

❌ Hardcoding secrets
❌ Forgetting to load dotenv
❌ Using wrong variable names

11. Summary

• Environment variables store configuration data

• Accessed via process.env

• dotenv simplifies management

• Essential for secure Node.js applications