Length of Rectangles on a page in InDesign CS5 js

Question

Hi, I need to have amount of rectangles on specific layer on specific page, and it doesn't work together:
myBackRectangles = myDoc.pages[1].rectangles.length(myDoc.layers.item ("Layer 1"));
It gives me length of the rectangles on all layers, but I need specific layer and that doesn't work.
Thank you for your help.
Yulia

Answer 1

I can spot one possible cause of bad behavior: the list myBackRectangles should be processed from last to first. If you remove a page containing one of these rectangles, the order will get messed up
So I thought this would do the trick
for (var a =myBackRectangles.length-1; a>=0; a--)
.. but .. it does not.
Some further head-scratching later I changed the alert to this
alert (myBackRectangles[a].parent.index+"; page "+myBackRectangles[a].parent.name);
where the 'name' displays the actual page number as seen in InDesign. Confusion! For some reason the page index of all pages is '0'!
I think this has to do with spreads. Internally, each page is 'on a spread' (even when it's only one single page), and therefore it's the first page on that spread (with index 0). The spread itself has another index, and that leads to yet another problem! In a facing page document, the spread index 1 contains pages 2 and 3, spread index 2 contains pages 4 and 5, and so on.
So you cannot use 'index' to check for a specific page in a document with facing pages. With no facing pages, you can use parentPage.parent.index -- which gives you the index of its spread.
If you have a facing pages document ... I don't know how to do this! <- Scratch This!
Hip hip hooray! I thought I had seen it somewhere before.
Don't use 'index' for a page because that doesn't work. Use documentOffset instead! ("The sequential number of the page within the document.", says the Help.)
I cannot test for CS5, but this ought to work slightly better:
myBackRectangles = myDoc.layers.item ("Layer 1").rectangles;
    for (var a = myBackRectangles.length-1; a>=0; a--){
          alert (myBackRectangles[a].parentPage.documentOffset);
        if (myBackRectangles[a].parentPage.documentOffset == 1){
            var myArtBack = myBackRectangles[a].graphics[0];
            if (myArtBack.isValid == false){
                myDoc.pages[1].remove();