No matter how much I use these technologies, I still seem to forget just enough that I regularly need to look up random stuff like how to iterate through an array, or what's the exact method name if I want to perform a fold/reduction and the exact order of the lambda's parameters. The problem gets worse if I switch between languages or don't use a language for an extended period of time.
I've gotten tired of the constant googling and navigating of documentation for the simplest of things. It doesn't help that the official documentation or otherwise resources I like often have poor SEO. These cheatsheets are my way of solving that problem for myself.
My cheatsheets aren't intended for someone to learn from scratch. If you're interested in those kinds of cheatsheets, check out Learn X in Y minutes. They're really nice!
You may notice that I might be missing a lot of very basic things. Sometimes, I just don't bother putting things that I rarely forget. In these cases, I think it's enough for me to just refer to the documentation.