This whole project that was uploaded in this last section on Deploying to Production, can be forked or cloned from GitHub.
Actually, I have many branches on that repository you might also like to try.
To download the ballgame branch,
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Open your browser and visit http://127.0.0.1:3000
You can improve this project by modifying it anyway you wish to make it into a game that you or other people may enjoy to play.