Saving a variable as a user or script property is an essential feature of Google Apps Script. However, it is one I didn’t use for months because I found it too complicated. Eventually it clicked, I use the properties feature in Apps Script regularly. Having hunted for tutorial and found little, I made this video to share what I learned, hopefully making it easier for others. The video walks through step-by-step how to create user and script properties in Google Apps Script.
Feel free to copy / steal / edit / mock the code to your liking.