Node.js Environment Variables
What are Environment Variables?
Environment variables are dynamic named values that can affect how running processes behave on a computer.
They are part of the environment in which a process runs and are used to configure applications without changing the code.
Key Benefits:
- Store configuration separate from code
- Keep sensitive information out of version control
- Configure applications differently across environments
- Change application behavior without code changes
Common Use Cases
Environment Configuration
- Database connection strings
- API keys and secrets
- External service URLs
- Feature flags
Runtime Behavior
- Logging verbosity
- Port numbers
- Timeouts and limits
- Environment-specific settings
Accessing Environment Variables in Node.js
Node.js provides the process.env object to access environment variables.
This object contains all the environment variables available to the current process.
Basic Usage
// Access a single environment variable
const nodeEnv = process.env.NODE_ENV || 'development';
console.log(`Running in ${nodeEnv} mode`);
// Access multiple variables with destructuring
const { PORT = 3000, HOST = 'localhost' } = process.env;
console.log(`Server running at http://${HOST}:${PORT}`);
// Check if running in production
if (process.env.NODE_ENV === 'production') {
console.log('Production optimizations enabled');
// Enable production features
}
Common Built-in Environment Variables
| Variable | Description | Example |
|---|---|---|
NODE_ENV |
Current environment (development, test, production) | production |
PORT |
Port number for the server to listen on | 3000 |
PATH |
System path for executable lookup | /usr/local/bin:/usr/bin |
HOME |
User's home directory | /Users/username |
Note: Always provide default values when accessing environment variables to prevent undefined values in your application.
Setting Environment Variables
There are several ways to set environment variables for your Node.js application, depending on your development workflow and deployment environment.
1. Command Line (Temporary)
Set variables directly in the command line when starting your application:
Windows (Command Prompt)
set PORT=3000
set NODE_ENV=development
set DB_HOST=localhost
node app.js
Windows (PowerShell)
$env:PORT=3000
$env:NODE_ENV="development"
node app.js
macOS/Linux (Bash/Zsh)
PORT=3000 NODE_ENV=development DB_HOST=localhost node app.js
macOS/Linux (Multiple Lines)
export PORT=3000
export NODE_ENV=development
node app.js
2. Using .env Files with dotenv
For development, use a .env file to store environment variables locally:
1. Install dotenv package
npm install dotenv
2. Create a .env file
# .env
PORT=3000
NODE_ENV=development
DB_HOST=localhost
DB_USER=admin
DB_PASS=your_secure_password
API_KEY=your_api_key_here
3. Load .env in your application
// Load environment variables from .env file
require('dotenv').config();
const port = process.env.PORT || 3000;
const dbConfig = {
host: process.env.DB_HOST,
user: process.env.DB_USER,
password: process.env.DB_PASS
};
console.log(`Server running on port ${port}`);
Important: Never commit .env files to version control. Add .env to your .gitignore file.
3. Production Environment Variables
In production, set environment variables using your hosting provider's configuration:
Heroku
heroku config:set NODE_ENV=production DATABASE_URL=your_database_url
Docker
docker run -e NODE_ENV=production -e PORT=3000 your-image
Linux/Systemd Service
# /etc/systemd/system/your-app.service
[Service]
Environment="NODE_ENV=production"
Environment="PORT=3000"
Using dotenv for Local Development
The dotenv package lets you load environment variables from a .env file:
# .env file
API_KEY=abcdef12345
Load the variables in your app:
require('dotenv').config();
console.log(process.env.API_KEY);
Install dotenv with:
npm install dotenv
Summary
Environment variables help you keep sensitive data and configuration out of your code.
Use process.env and tools like dotenv to manage them easily in Node.js.
