It looks like a bug was introduced in jquery 2.2.0 with the 'on' function.

If you have code that registers a bunch of handlers in a chain and one of the callbacks is null, the on function will return the window object when the callback is null which causes the chaining to fail. This works with jquery 2.1.4. After a little investigation, it looks like the 'on' method was refactored to be global within jquery's scope and returns this (which used to be the jquery object but now is window).

//example from jquery impromptu plugin
$('.selector').on("keydown",keyDownEventHandler)
.on('impromptu:loaded', opts.loaded)
.on('impromptu:close', opts.close)
.on('impromptu:statechanging', opts.statechanging)
.on('impromptu:statechanged', opts.statechanged);