jQuery :focus Selector
Learn all about the jQuery function :focus Selector.
As with other pseudo-class selectors (those that begin with a ":"), it is recommended to precede
:focus with a tag name or some other selector; otherwise, the universal selector ( "*" ) is implied. In other words, the bare
$( ":focus" ) is equivalent to
$( "*:focus" ). If you are looking for the currently focused element,
$( document.activeElement ) will retrieve it without having to search the whole DOM tree.