Node.js Lesson 12: Environment Variables

Environment variables keep secrets (API keys, passwords, database URLs) out of your code. Never hardcode secrets. Never commit .env to git.

dotenv Setup

npm install dotenv

# Create .env file in project root:
PORT=3000
DB_URL=mongodb://localhost:27017/mydb
JWT_SECRET=my_super_secret_key_change_this
API_KEY=sk-abc123
NODE_ENV=development

# CRITICAL: add .env to .gitignore!
echo ".env" >> .gitignore

Using Environment Variables

// At the TOP of your entry file (app.js)
require("dotenv").config();

// Now process.env has all your .env variables
const PORT = process.env.PORT || 3000;
const DB_URL = process.env.DB_URL;
const JWT_SECRET = process.env.JWT_SECRET;
const isDev = process.env.NODE_ENV === "development";

if (!DB_URL) {
  console.error("FATAL: DB_URL not set!");
  process.exit(1);
}

app.listen(PORT, () => {
  console.log(`Server on port ${PORT} [${process.env.NODE_ENV}]`);
});

Config Module Pattern

// config/index.js — centralize all config
require("dotenv").config();

module.exports = {
  port: Number(process.env.PORT) || 3000,
  db: {
    url: process.env.DB_URL,
    name: process.env.DB_NAME || "myapp"
  },
  jwt: {
    secret: process.env.JWT_SECRET,
    expiresIn: process.env.JWT_EXPIRES || "7d"
  },
  isDev: process.env.NODE_ENV !== "production"
};

// In any other file:
const config = require("./config");
app.listen(config.port);