var arr = document.getElementById('valAtags').getElementsByTagName('a');
for(var i = 0 ; i < arr.length ; i++){
arr[i].attachEvent('onclick', setActive);
}

var akt = "";

function setActive(event){
if(akt!=""){
akt.setAttribute('id', 'inaktiv');
akt.previousSibling.setAttribute("id", "inaktiv");
event.srcElement.parentNode.setAttribute("id", "aktiv");
}
event.srcElement.setAttribute("id", "aktiv");
event.srcElement.previousSibling.setAttribute("id", "aktiv");
event.srcElement.parentNode.setAttribute("id", "aktiv");
akt = event.srcElement;
}