function selectGroup(){
var sel = document.getElementById('userGroups');
alert(sel.options[sel.selectedIndex].text);
}
or
<s:select
id="userGroups"
headerKey="-1"
headerValue="------ Select Group ------" list="userGroupList"
listValue="groupName"
onchange="selectGroup(this)">
function selectGroup(sel){
alert(sel.options[sel.selectedIndex].text);
}
or
<s:select
id="userGroups"
headerKey="-1"
headerValue="------ Select Group ------" list="userGroupList"
listValue="groupName"
onchange="alert(this.options[this.selectedIndex].text);">