How to manage environment variables in Node.js?

// Access via process.env
const port = process.env.PORT || 3000;
const dbUrl = process.env.DATABASE_URL;
const nodeEnv = process.env.NODE_ENV;

console.log(process.env); // All env variables

npm install dotenv

# .env file
PORT=3000
DATABASE_URL=mongodb://localhost:27017/mydb
JWT_SECRET=mysecretkey
NODE_ENV=development

// Load at app start
require('dotenv').config();

// Or with ES modules
import 'dotenv/config';

// Now access variables
const port = process.env.PORT;

const Joi = require('joi');

const envSchema = Joi.object({
  NODE_ENV: Joi.string().valid('development', 'production', 'test').required(),
  PORT: Joi.number().default(3000),
  DATABASE_URL: Joi.string().required(),
}).unknown();

const { error, value } = envSchema.validate(process.env);

if (error) {
  throw new Error(`Config validation error: ${error.message}`);
}

module.exports = {
  env: value.NODE_ENV,
  port: value.PORT,
  dbUrl: value.DATABASE_URL,
};