Environment Variables in Node.js

Learn how to store configuration values, database credentials, API keys, and other application settings using environment variables.

1. What Are Environment Variables?

Environment variables are named values available to a running application. They help us configure an application without writing environment-specific settings directly into the source code.

For example, an application may need these values:

PORT=3000
DB_HOST=localhost
DB_USER=root
DB_PASSWORD=my_database_password
JWT_SECRET=your_secret_value

2. Why Do We Need Environment Variables?

const PORT = 3000;
const DB_PASSWORD = "mySecretPassword";

const PORT = process.env.PORT;
const DB_PASSWORD = process.env.DB_PASSWORD;

3. What Is process.env?

Node.js provides the process.env object to access environment variables available to the running process.

console.log(process.env.PORT);
console.log(process.env.NODE_ENV);

3000
development

4. Create a Node.js Project

Open your terminal and create a project folder.

mkdir node-env-demo
cd node-env-demo
npm init -y

Your project will contain these files:

node-env-demo/
│
├── package.json
├── .env
├── .gitignore
└── app.js

5. Create a .env File

A .env file stores configuration values as NAME=value pairs. Create a file named .env in your project folder.

PORT=3000
APP_NAME=Soopro Pathshala
NODE_ENV=development

6. Install dotenv

The dotenv package loads variables from your .env file into process.env.

npm install dotenv

7. Read Environment Variables in Node.js

Create a file named app.js.

require('dotenv').config();

const appName = process.env.APP_NAME;
const port = process.env.PORT;
const environment = process.env.NODE_ENV;

console.log('Application:', appName);
console.log('Port:', port);
console.log('Environment:', environment);

Run the Program

node app.js

Output

Application: Soopro Pathshala
Port: 3000
Environment: development

The dotenv.config() call loads the file before the application reads its variables.

8. Use Environment Variables in an Express Server

Environment variables are often used to configure the port of an Express server.

Install Express

npm install express

Create server.js

require('dotenv').config();

const express = require('express');
const app = express();

const PORT = Number(process.env.PORT) || 3000;

app.get('/', (req, res) => {
    res.send('Welcome to Soopro Pathshala Node.js Tutorial!');
});

app.get('/about', (req, res) => {
    res.json({
        application: process.env.APP_NAME || 'Node.js Application',
        environment: process.env.NODE_ENV || 'development'
    });
});

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

Run the Server

node server.js

Open the following URLs in your browser:

• http://localhost:3000/
• http://localhost:3000/about

9. Protect Your .env File Using .gitignore

If you use Git, prevent your local .env file from being committed to the repository.

Create a file named .gitignore:

.env
node_modules/

10. Store Database Credentials in Environment Variables

Database connection details should come from configuration rather than being written directly into your application code.

.env

DB_HOST=localhost
DB_USER=root
DB_PASSWORD=replace_with_your_database_password
DB_NAME=school_db

Read the Configuration

require('dotenv').config();

const dbConfig = {
    host: process.env.DB_HOST,
    user: process.env.DB_USER,
    password: process.env.DB_PASSWORD,
    database: process.env.DB_NAME
};

console.log('Database host:', dbConfig.host);
console.log('Database name:', dbConfig.database);

11. Environment Variables for JWT Secrets

In the previous lesson, you learned about JWT authentication. A JWT signing secret should be supplied through a secure environment configuration instead of being hardcoded.

.env

JWT_SECRET=replace_with_a_long_random_secret

Node.js Example

require('dotenv').config();

const jwtSecret = process.env.JWT_SECRET;

if (!jwtSecret) {
    throw new Error('JWT_SECRET is not configured');
}

// Use jwtSecret with your JWT library.
// Never print the secret or send it to the client.

12. Use Default Values

Sometimes an environment variable may not be configured. You can supply a default for non-sensitive settings.

const PORT = Number(process.env.PORT) || 3000;

const APP_NAME =
    process.env.APP_NAME || 'My Node.js Application';

console.log(APP_NAME);
console.log(PORT);

For example, if PORT is not set, the program uses port 3000.

13. Environment Variables Are Strings

Values read from process.env are strings. Convert them before using them as numbers or booleans.

const port = Number(process.env.PORT || 3000);

const maintenanceMode =
    process.env.MAINTENANCE_MODE === 'true';

console.log(typeof port);       // number
console.log(maintenanceMode);   // true or false

14. Set Environment Variables Without a .env File

Environment variables can also be supplied by the terminal or hosting platform.

Windows Command Prompt

set PORT=4000
node server.js

PowerShell

$env:PORT="4000"
node server.js

Linux or macOS

PORT=4000 node server.js

These examples set the variable for the process launched from that terminal. The exact scope and syntax depend on the operating system and shell.

15. Common Mistakes

16. Practical Assignment

17. Summary

• Environment variables store application configuration.
• process.env accesses variables in Node.js.
• The dotenv package loads values from a .env file.
• Use environment variables for ports and database configuration.
• Protect secrets and keep local .env files out of Git.
• Use secure hosting configuration for production secrets.
• Validate and convert environment variable values when needed.