How to Use dotenv in Node.js for Environment Variables

Use the dotenv package in Node.js by installing it with npm install dotenv, creating a .env file with your variables, and loading them at the start of your app with require('dotenv').config(). This makes environment variables accessible via process.env in your code.

Syntax

To use dotenv, first import and configure it at the very top of your main JavaScript file. This loads variables from a .env file into process.env.

• require('dotenv').config(): Loads the environment variables.
• .env file: Stores key-value pairs like KEY=value.
• process.env.KEY: Accesses the variable in your code.

javascript

require('dotenv').config();

console.log(process.env.MY_VARIABLE);

Output

value_of_MY_VARIABLE

Example

This example shows how to create a .env file, load it with dotenv, and use the variables in your Node.js app.

javascript

// 1. Create a .env file in your project root with:
// PORT=3000
// SECRET_KEY=mysecret

// 2. Create index.js with:
require('dotenv').config();

const port = process.env.PORT;
const secret = process.env.SECRET_KEY;

console.log(`Server will run on port: ${port}`);
console.log(`Secret key is: ${secret}`);

Output

Server will run on port: 3000
Secret key is: mysecret

Common Pitfalls

Common mistakes when using dotenv include:

• Not calling require('dotenv').config() before accessing process.env.
• Placing the .env file in the wrong directory (it should be in the project root).
• Committing .env to version control, which can expose secrets.
• Forgetting to restart the Node.js app after changing .env.

javascript

// Wrong: Accessing process.env before loading dotenv
console.log(process.env.PORT); // undefined
require('dotenv').config();

// Right: Load dotenv first
require('dotenv').config();
console.log(process.env.PORT); // '3000' if set in .env

Output

undefined
3000

Quick Reference

Step	Command / Action	Description
1	npm install dotenv	Install dotenv package
2	Create .env file	Add key=value pairs for environment variables
3	require('dotenv').config()	Load variables at app start
4	process.env.KEY	Access variables in code
5	Add .env to .gitignore	Prevent secrets from being committed

Key Takeaways

Always call require('dotenv').config() before using process.env variables.

Store environment variables in a .env file at your project root.

Never commit your .env file to version control to keep secrets safe.

Restart your Node.js app after changing environment variables.

Access variables in code using process.env.VARIABLE_NAME.