JavaScript - Detecting Caps lock

I wanted to see if you could detect caps lock in JavaScript. Why? As a small usability touch, basically alerting users that caps lock is enabled when they are entering passwords for example. I’ve wrapped up the logic in a simple function that can help you detect caps lock on a key press.

Sorry. Demo no longer exists, just copy the code and it should work straight off ;)

function isCapslock(e){

    e = (e) ? e : window.event;

    var charCode = false;
    if (e.which) {
        charCode = e.which;
    } else if (e.keyCode) {
        charCode = e.keyCode;
    }

    var shifton = false;
    if (e.shiftKey) {
        shifton = e.shiftKey;
    } else if (e.modifiers) {
        shifton = !!(e.modifiers & 4);
    }

    if (charCode >= 97 && charCode <= 122 && shifton) {
        return true;
    }

    if (charCode >= 65 && charCode <= 90 && !shifton) {
        return true;
    }

    return false;

}