In Suicide Squad we see Joker's car crash, and then Batman jumps into the water, but only sees Harley. Where did Joker go? Did he just swim away? Did he use an unseen eject button?
He escaped. There was no ejection seat as the seat is still there and the roof is intact. He obviously swam away while Batman pulled Harley out from the front windshield where she was stuck.
He escaped and saved his life leaving Harley Quinn behind.
It seems that this JOKER is also good at escape art.
In that helicopter blast scene, Joker saved himself.