Show a little capslock warning if the user tries to log in while their capslock key is on.

capslockwarning.js

<script>
    (function() {
        var capsLockEnabled = false;

        document.onkeypress = function (e) {
            e = e || window.event;
            var s = String.fromCharCode(e.keyCode || e.which);
            if (s.toLowerCase() === s.toUpperCase()) {
                return;
            }

            capsLockEnabled = s.toUpperCase() === s && !e.shiftKey;
            _showCapsAlert();
        }

        document.onkeydown = function (e) {
            e = e || window.event;
            if (e.keyCode === 20) {
                capsLockEnabled = !capsLockEnabled;
            }
            _showCapsAlert();
        }

        function _showCapsAlert() {
            var warningEl = document.getElementById('capsWarning');
            if (warningEl == null) {
                return;
            }

            if (capsLockEnabled) {
                warningEl.style.visibility = 'visible';
            } else {
                warningEl.style.visibility = 'hidden';
            }
        }

    })();

</script>

This isn't perfect... like if you go to the page with capslock on and then turn it off, it only knows that you changed capslock state so it shows the warning. If you go with it on and then type something, it will prompt and let you know. if you load the page with capslock off and then turn it on (like I do all of the time when I'm hitting that a key), then it will show the warning.