Heroku Deployment Pitfall: Bind to $PORT
During development, you set a port that Node listens to.
That doesn't work with Heroku because Heroku binds your port and you cannot set it yourself.
You'll get an error:
Web process failed to bind to $PORT within 60 seconds of launch.
Fix this with environment variable
const PORT = process.env.PORT || 5000 app.listen(PORT)