[ruslan_mart]

var myVar = document.getElementsByClassName('a');

myVar[0].parentNode.addEventListener('click', function(e) {
   var self = e.target;
   if(self.className != 'a') return;
   var i = myVar.length;
   while(i--) {
      if(myVar[i] == self) {
         var x = i;
         break;
      }
   }

   alert(x);
});