I'm working in Google Sheets. I'm using an app script that I adapted from this youtube video and it is working well; it copies information from one document to another whenever I click on a customised menu item. The only issue I am having is that every time I select this menu item, it doesn't differentiate the already-copied information from the never-copied information. Therefore, the second document ends up with duplicate values.
Is there a way to code the app script so that it recognises duplicates and doesn't copy them over? I don't mind if this removes the menu item function (i.e. if instead the script is triggered by onEdit, for example), I just need a way to stop the duplication.
