Sorry for the late reply – you can compare with “Author” and “Editor” in this trigger (see attachment).
If you want to use Custom JS you can find the author like this:
// Name
spjs.dffs.beforeProperties.Author
["Alexander Bautz"]
// ID
spjs.dffs.beforeProperties.Author_ID
["12"]
Please note that both values are in fact arrays so you must convert it to string if you plan to use it for comparing with another variable.
Alexander