heroku-node-procfile.md

You don't need a Procfile for simple Node.js apps on Heroku. Simply add a start script to your package.json:

{
  "scripts": {
    "start": "node index.js"
  }
}

This will work locally too: npm start.

If you would like to run with a slightly different setup in development (e.g. using nodemon to automatically restart your server on changes) try this:

{
  "scripts": {
    "dev": "nodemon index.js",
    "start": "node index.js"
  }
}

Note that npm start is a shortcut for npm run start which doesn't exist for keys so for your dev task you will have to run npm run dev.