The FocusEvent() constructor returns a newly created FocusEvent object with an optional EventTarget. When a change a focus has a source and a destination, the relatedTarget value must be set to the other target.
var focusEvent = new FocusEvent(typeArg, focusEventInit);
The FocusEvent() constructor also inherits arguments from UIEvent() and from Event().
Is a DOMString representing the name of the event.
Is a FocusEventInit dictionary, having the following fields:
"relatedTarget", optional and defaulting to null, is an EventTarget representing the secondary target of a FocusEvent.