dotenv-flow automatically loads multiple .env files based on NODE_ENV: .env (base), .env.local (local overrides), .env.${NODE_ENV} (environment-specific), and .env.${NODE_ENV}.local. Later files override earlier ones, providing flexible environment management.
Use ${VAR_NAME} syntax. For example, BASE_URL=https://api.yourdomain.com and API_URL=${BASE_URL}/api/v1. When dotenv loads, API_URL becomes https://api.yourdomain.com/api/v1. This avoids duplication.
Use the envalid package. Define a schema with types (str, num, bool, url, email), choices, defaults, and minLength. cleanEnv validates all variables, type-casts them, provides defaults, and throws an error at startup if validation fails.
Set boolean env vars like ENABLE_EMAILS=true, ENABLE_CHAT=true. In code, check if (config.ENABLE_EMAILS) before sending emails. This lets you enable/disable features without code changes useful for staging testing and gradual rollouts.
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