Determine whether Caps Lock is ON in ASP.net Page by JavaScript

Here I used a simple Textbox in ASP.net page and used Javascript to determine whether Caps Lock is on or off.
I have used the following Javascript code in between head  tag.
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) {
                document.getElementById("txtCapsMsg").value = "Caps Lock is on";
                return true;
            }

            if (charCode >= 65 && charCode <= 90 && !shifton) {
                document.getElementById("txtCapsMsg").value = "Caps Lock is on";
                return true;
            }

            document.getElementById("txtCapsMsg").value = "Caps Lock is off";
            return false;

        }

I have also used two text box in ASP.net page. One for input and another for displaying message whether Caps Lock is on or off.

Message :
Input Text :

Now input some text in input textbox. Message will be showed in txtCapsMsg, textbox whether Caps Lock is on or off.