The Jack-in-the Box is a powerful spring like device used by the Joker. It can lift the person up to a very high feat when it's platform or a hidden button on it is stepped on. The stronger the spring, the higher you go.
History[]
In the television series, the Joker used this device as a way to escape from Gotham State Penitentiary. He built it in the pen's metal shop and craftily hid it under the pitcher's mound where a softball game would be taking place. He then "sprung himself", leaving behind a bust of himself under the base of the spring to taunt Batman.
In the movie, he was a member of the criminal organization United Underworld, along with the Penguin, the Riddler and the Catwoman.
Riddler came up with a plan to attack Batman and Robin at their hideout. Joker would build another Jack-in-the Box which would shoot them through a window out over the sea into an exploding octopus made by Penguin, which would blow them to bits, leaving nothing to link them to their involvement.
They unfortunately chose Bruce Wayne as a hostage as part of their plan to lure the Dynamic Duo to them, unaware he was the true identity of their actual enemy Batman himself. During a fight, one of their henchmen fell on the Jack-in-the Box, shooting him out of the window into Penguin's exploding octopus, giving him what they had intended for Batman.