Get app.documents[???] for the activeDocument

Question

An example:
I have 10 opened images in photoshop.
I start working on the last one, then the one before, and so on until the 8th image.
1, 2, 3, 4, 5, 6 are opened
7, 8, 9 are finished and must be saved.
I want an action that will save the activeDocument and all the ones after that: in the example will save the 7th 8th and 10th image.
Is this possible?
I have everything but I don't know how to get the number for the activeDocument >>> app.documents[???]

Answer 1

The quick way doesn't always work.
For instance:
1) File > New...
2) 3D > New Shape From Layer > Cube Wrap
3) Image > Duplicate...
Then run your code (slightly modified):
function getActiveDocumentIndex(){
     var ref = new ActionReference();
     ref.putEnumerated( charIDToTypeID("Dcmn"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
     return desc = executeActionGet(ref).getInteger(stringIDToTypeID('itemIndex'))-1;
var index = getActiveDocumentIndex();
alert('The activeDocument is app.documents['+getActiveDocumentIndex()+']');
alert(app.documents[index].name);
It thinks the duplicated doc is [2] instead of [1] then fails when you try to get the name. This is apparently an artifact of the 3D system introducing new pseudo-documents internally when you have 3D layers.
You end up have to use something like this to get the actual DOM index:
function getDocumentIndex(doc) {
  var docs = app.documents;
  for (var i = 0; i < docs.length; i++) {
    if (docs[i] == doc) {
      return i+1;
  return -1;
This is a CS5/Extended problem but the problem may present itself in other ways.