The relatedTarget read-only property of the FocusEvent interface is the secondary target, depending on the type of event:Event name targetrelatedTargetblurThe EventTarget losing focusThe EventTarget receiving focus (if any).focusThe EventTarget receiving focusThe EventTarget losing focus (if any)focusinThe EventTarget receiving focusThe EventTarget losing focus (if any)focusoutThe EventTarget losing focusThe EventTarget receiving focus (if any)
Note that many elements can't have focus, which is a common reason for relatedTarget to be null. relatedTarget may also be set to null for security reasons, like when tabbing in or out of a page.
MouseEvent.relatedTarget is a similar property for mouse events.
An instance of EventTarget.