Detect which form input has focus using JavaScript or jQuery

Question

How do you detect which form input has focus using JavaScript or jQuery?

From within a function I want to be able to determine which form input has focus. I'd like to be able to do this in straight JavaScript and/or jQuery.

Answer 1

document.activeElement, it's been supported in IE for a long time and the latest versions of FF and chrome support it also. If nothing has focus, it returns the document.body object.