get li index within a ul not with jquery!

I'm using dhtmlgoodies drag-drop-folder-tree and when you click save you get the

id-parentid, id-parentid, etc...

i want to have the li index within it's ul so i can tell their order as well - so i want it to look like this:

id-parentid-orderid, id-parentid-orderid, ETC...

their code is not jquery (i know how to do it in jquery with the index() but it is pure JS

how do i get the index of an element within his parent?

You'll have to write your own index function ;)

e.g. lets say that liNode is an <li> node within an <ul>

function index(array, element) {
   for (var i = 0; i < array.length; i++) {
      if (array[i] == element) return i;
      i++;
   }
   return -1;
}

var allLiNodes = liNode.parentNode.childNodes;
var myIndex = index(allLiNodes, liNode);