<html>
<head>
<script language="JavaScript">
function setLabel()
{
document.getElementById('setMe').innerHTML = 'set it to this';
}
</script>
</head>
<body>
<p id="setMe"></p>
<a href="javascript: setLabel();">Set the label</a>
</body>
</html>
That shows you how to set the label. You should be able to use that technique with whatever Javascript you have in place.
Javascript is client-side scripting, so I'm going to put this into that forum.