var itemsByIndex  = [];
var itemsByObject = [];

items = document.body.getElementsByTagName('li');
for (var i=0; i<items.length; i++) {
  itemsByIndex[i] = items[i];
  itemsByObject[items[i]] = i;
}
window.status = 'itemsByIndex:' + itemsByIndex.length + ', ItemsByObject:' + itemsByObject.length;

// itemsByIndex shows the proper count but itemsByObject is empty?