.env

FOO=bar

index.js

console.log(process.env.FOO);

package.json

{
  "scripts": {
    "start": "node -r dotenv-extended/config index.js",
    "dev": "nodemon -r dotenv-extended/config index.js"
  },
  "dependencies": {
    "dotenv-extended": "^2.0.1",
    "nodemon": "^1.12.7"
  }
}