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

Answer 1

I would do it this way: I used a function that would return a 1 if the ID of the element it was sent was one that would trigger my event, and all others would return a 0, and the "if" statement would then just fall-through and not do anything:

function getSender(field) {
    switch (field.id) {
        case "someID":
        case "someOtherID":
            return 1;
        break;
        default:
            return 0;
    }
}

function doSomething(elem) {
    if (getSender(elem) == 1) {
       // do your stuff
    }
  /*  else {
       // do something else
    }  */
}

HTML Markup:

The first two will do the event in doSomething, the last one won't (or will do the else clause if uncommented).

-Tom