CollisionViz is a data visualization app which shows car crashes in the New York City. I wrote it when I was at AppAcademy in 2017. Since then, I haven't spent a lot of time on it. Recently I found out that it stopped working. Software is like cars - it needs maintainable. In addition to fixing it, I gave it an overhaul. Below are some advice that I wise I knew when I first wrote CollisionViz, and hopefully it is applicable to other new programmers.