sortable lists in knockout.js

sortablelist.js

ko.bindingHandlers.sortableList = {
    init: function(element, valueAccessor, allBindingsAccessor, context) {
        var parent = allBindingsAccessor().parent
        var list = valueAccessor();
        $(element).sortable({
            handle : '.move'
            ,start: function(){ mpq.track("sort")}
            ,sort: function(){
                var $lis = $(this).children('li');
                $lis.each(function(){
                    var $li = $(this);
                    var hindex = $lis.filter('.ui-sortable-helper').index();
                    if( !$li.is('.ui-sortable-helper') ){
                        var index = $li.index();
                        index = index < hindex ? index + 1 : index;

                        $li.val(index);

                        if( $li.is('.ui-sortable-placeholder') ){
                            $lis.filter('.ui-sortable-helper').val(index);
                        }
                    }
                });
            }
            ,update: function(event, ui) {
                //retrieve our actual data item
                var item = ko.dataFor(ui.item[0]);

                //figure out its new position
                var position = ko.utils.arrayIndexOf(ui.item.parent().children(), ui.item[0]);


                //remove the item and add it back in the right spot
                if (position >= 0) {
                    list.remove(item);
                    list.splice(position, 0, item);
                }
                ui.item.remove();
                parent.save(App.VMs.course)
            }
        });
    }
};