How to Select the Document just back of the Active Document

Question

If there are 5 documents open in photoshop I want to select the document just behind or back of the Active Document , using script.
One of my friend suggested me the bleow script, but it is selecting the previous document, not exactly the document back of the active document.
please help me.
var id85 = charIDToTypeID( "slct" );
    var desc21 = new ActionDescriptor();
    var id86 = charIDToTypeID( "null" );
        var ref11 = new ActionReference();
        var id87 = charIDToTypeID( "Dcmn" );
        ref11.putOffset( id87, -1 );
    desc21.putReference( id86, ref11 );
executeAction( id85, desc21, DialogModes.NO )

Answer 1

I had the same problem. I did not want to go back to the "last viewed" doc but to the doc opened before the active one.
I use this on F1 key to go back to the previous opened document (index order -1).
It works great.
#target photoshop
// Go back to the last opened doc. If it is the oldest opened one it does not give error window and stays on it.
if(documents.length>0) {
    var thisIndexImage = getActiveDocumentIndex();
    var theDocs = app.documents;
    if ( thisIndexImage != 0 ) {
        var openedBefore = theDocs[thisIndexImage - 1];
        } else {
        var openedBefore = theDocs[0];
    app.activeDocument = openedBefore;
} else {
    alert ("You need to have any opened documents to apply this script.")
// Functions
function getActiveDocumentIndex(){
     var ref = new ActionReference();
     ref.putEnumerated( charIDToTypeID("Dcmn"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
     return desc = executeActionGet(ref).getInteger(stringIDToTypeID('itemIndex'))-1;