I have been reading a book about real English expressions and idioms. The first chapter deals with greetings. According to the section On departure,
See you later, alligator
is one of the informal ways of saying goodbye to someone.
The book says that it's humoristic and the answer would be in a while crocodile. Apparently, it's derived from a 50s pop song.
My question is: Is this expression common? It goes without saying that I am not a native speaker of English but I usually listen to English music, films and TV shows and I have never heard of it before.