Subfolders

var myFolder = Folder.selectDialog("Select your folder containing the files", "");
f = find_files(myFolder);

function find_files (dir)
    {
    return find_files_sub (dir, []);
    }

function find_files_sub (dir, array)
    {
    var f = Folder (dir).getFiles ("*.*");
    for (var i = 0; i < f.length; i++)
        {
        if (f[i] instanceof Folder)
            find_files_sub (f[i], array);
        else
            if (f[i].name.slice (-3).toLowerCase() == ".ai")
                array.push (f[i]);
        }
    return array;
    }