I have a personal project ive worked on a lot last year. There was a part in my code which at the time scared me a bit because of the complicated data organization and manipulation that was going on. When I first wrote it, I had to have a clear picture in my kind about what properties an object had and what their properties had and do on. I had to write this down all on paper.

This year, when I came back to the code. I converted everything to typescript. I made sure that every variable that my manipulation worked on had a type. It not only helped me remember how the code worked but it made it so much easier to understand it and modify it without fear of breaking things.

It's been super useful and I don't think I'll be writing any big programs in the future without it.