Environment Variables

Environment variables store config and secrets (API keys, database URLs) outside your code. Node reads them from process.env. Keep them in a .env file and add .env to .gitignore so secrets never reach GitHub.

# .env
PORT=3000
DATABASE_URL=postgres://user:pass@localhost:5432/app

// server.js (Node 20+ can load .env with --env-file)
// node --env-file=.env server.js
const port = process.env.PORT || 3000
console.log(process.env.DATABASE_URL)

# .gitignore
.env