firefox addone SDK: basic extension: what is the {} for?

Question

var { ActionButton } = require("sdk/ui/button/action");

what is the {} for ?

Looks like panels do not need that

var panel = require("sdk/panel").Panel({
  width: 180,
  height: 180,
  contentURL: "https://en.wikipedia.org/w/index.php?title=Jetpack&useformat=mobile"
});