I originally built this in Processing (source).

I converted it to run in p5.js so I could showcase it here, without having to download anything. I'm not sure why there's a white bar on the left tbh.

If you want to run the original Processing version, you'll have to install the Processing editor first, and then open Pong.pde as a project.

Controls: W and S control the left paddle, up and down arrows control the right paddle.