What are Environment Variables?

👀 Introduction to Environment Variables

Environment variables are key-value pairs used to configure your application from outside your source code.

Why Use Them?

• 🔒 Security — hide sensitive data like API keys and database passwords.

• ⚙️ Flexibility — set different values for development, testing, and production without touching code.

• 🧼 Clean code — avoid hardcoding secrets and settings directly into files.

• 🚀 Portability — the same codebase runs correctly across different machines and deployment environments.

Example: Hardcoded vs Environment Variable

❌ Bad practice (hardcoding):

const dbPassword = "mySecret123";

• Anyone with access to the code sees the password.

• Changing environments (dev → production) means editing and redeploying code.

✅ Better with environment variables:

const dbPassword = process.env.DB_PASSWORD;

• The actual value lives outside the code, in a .env file (more below).

• Swapping environments just means swapping the .env file — no code changes.

🔧 Using process.env in Node.js

process.env is a built-in Node.js object that gives access to all environment variables currently set on the system.

console.log('Your system username is:', process.env.USERNAME);

• Every value on process.env is always a string — even numbers or booleans need manual conversion (Number(process.env.PORT)).

• If a variable isn't set, accessing it returns undefined, not an error — good to guard against with a default value.

📄 The .env File

A .env file stores environment variables locally, outside your source code, in simple KEY=value pairs.

DB_PASSWORD=mySecret123
PORT=3000
API_KEY=abc123xyz

• Lives at the root of your project.

• Node doesn't read .env files natively (in older versions) — you need the dotenv package to load it.

Setting It Up

npm install dotenv

require('dotenv').config();

console.log(process.env.DB_PASSWORD);
// 'mySecret123'

• .config() reads the .env file and loads every key into process.env.

• Call this as early as possible — ideally the very first line of your entry file — so every other file that runs afterward can access the variables.

💡 Node 20.6+ can load .env files natively with node --env-file=.env app.js, without needing dotenv at all.