How do you tell if caps lock is on using JavaScript?

<input autocomplete="off"  type="text" id="username" title="login" name="username" onkeypress="isCapLockOn(event)" class="width_100"><div id='username_error'style="display:none;"></div>


function isCapLockOn(e)
{
var charKeyCode = e.keyCode ? e.keyCode : e.which; // To work with both MSIE & Netscape
var shiftKey = e.shiftKey ? e.shiftKey : ((charKeyCode == 16) ? true : false);
// Check both the condition as described above
if (((charKeyCode >= 65 && charKeyCode <= 90) && !shiftKey)
|| ((charKeyCode >= 97 && charKeyCode <= 122) && shiftKey))
{
// Caps lock is on
document.getElementById('username_error').innerHTML = "Caps lock : <b>On</b>";
}
else
{
// Caps lock is off.
document.getElementById('username_error').innerHTML = "Caps lock : <b>Off</b>";
}

}