iirc from a book about the series (years ago, I don't still have it, alas), their general take on the Joker was "he's an aging rockstar" which is so brilliant -- a villain who's dangerous but appropriate for 8 year olds, petty and funny and vain and desperate for attention.
I'm glad BTAS understood that Joker is most fun when he's deeply petty. His best stories are rarely "tries to destroy Gotham" but rather "gets mad that someone cut him off in traffic" or "wants to copyright fish" or "bombed during stand-up" or "a casino stole his likeness."