:focus - get the currently focused element

jquery.ba-focus.js

// Public domain, really.

jQuery.expr[':'].focus = function( elem ) {
  return elem === document.activeElement && ( elem.type || elem.href );
};

@dperini:

Somebody argued that "type" is also an attribute of "script" and "style" elements.
I agree... but these elements are invisible so they would never become the document.activeElement :)

Unless someone would apply display: block to those elements [example].

@mathiasbynens,
ha...ha... what for ?
If you want to fake the test or the selector engine or the browsers CSS engine you will be able to do it under all circumstances. Just set the "type" or "href" property of each element in the page. The check could test the nodeName of valid focusable elements to make it stronger but it will be useful only for you and your non-standard approach and that has no value for me.

@dperini I wasn’t trying to be funny, just pointing it out. I very much agree it would be nonsensical to write additional code to take into account these weird and highly unlikely situations.

Should this maybe also check for some element that is not an input that has tabIndex ?

please you send me a sample how to use this selector (:focus) ?

It works like this: :focus selector (note that recent versions of jQuery include this selector)