Current Plex Genres:

Action
Adventure
Animation
Biography
Comedy
Crime
Documentary
Drama
Family
Fantasy
Film-Noir
History
Horror
Music
Musical
Mystery
Romance
Sci-Fi
Science Fiction
Sport
Thriler
TV Movie
War
Western

Also allow searching for a combination of genres, such as Action Adventure

Might be able to use something like the following:

plex.query("/library/sections/3/all?genre=2967")

But this would require checking the server mappings for the genres manually

Further Info:

https://github.com/phillipj/node-plex-api