$helper = new PaginationHelper(['a','b','c','d','e','f'], 4);
$helper->pageCount(); // 2
$helper->itemCount(); // 6
$helper->pageItemCount(0); // 4
$helper->pageItemCount(1); // last page 2
$helper->pageItemCount(2); // -1 since the page is invalid
// pageIndex takes an item index and returns the page that it belongs on
$helper->pageIndex(5); // 1 (zero based index)
$helper->pageIndex(2); // 0
$helper->pageIndex(20); // -1
$helper->pageIndex(-10); // -1
var helper = new PaginationHelper(['a','b','c','d','e','f'], 4);
helper.pageCount(); // 2
helper.itemCount(); // 6
helper.pageItemCount(0); // 4
helper.pageItemCount(1); // last page 2
helper.pageItemCount(2); // -1 since the page is invalid
// pageIndex takes an item index and returns the page that it belongs on
helper.pageIndex(5); // 1 (zero based index)
helper.pageIndex(2); // 0
helper.pageIndex(20); // -1
helper.pageIndex(-10); // -1