Array.observe lacks 'move' change type and Array.prototype lacks move(from, to) method

[alexanderby]

Since Array.observe may be used to bind some collection model to DOM elements, the move() method and move change type are needed to move the nodes associated with collection items. Currently it is only possible to handle addition, removal and replacement of collection items which leads to possibly unnecessary nodes removal and re-additions. Some example (works in Chrome): http://jsfiddle.net/alexanderby/fd0mrp8j/

As an example .NET's INotifyCollectionChange has such an action and ObservableCollection implements a Move method.

Also Array.prototype.sort() method should notify of move change type instead of update, as far as moved collection item may be collection itself and it's replacement may cause re-creation off associated DOM.

[alexanderby]

Seems I've found some not beautiful workaround. When going just to move one item, I'm storing from and to indices before splice and when the notification comes decide whether to move or add/remove nodes. This is ugly, but allows to work with tree structures without any complex observers (e.g. specifying index paths as from:[1, 3, 4], to:[1,2]). Edited previous example: http://jsfiddle.net/fd0mrp8j/7/

[alexanderby]

So, while creating an ObservableCollection (which implements Array interface) for a vector graphics editor's models I ended up with these change types Create, Replace, Delete, Move, Attach, Detach. Also I've extended Array.prototype with methods move(from, to), attach(item, index), detach(index). Collection notifies of index-properties change events ("0", "1"...) at the end of any method call. The Move change occurs when calling move(), sort() or reverse(). The Attachand Detach changes are used when manipulating tree-structures, so the subscriber may store it's detached node at it's holder (e.g. tree controller) or get an attached node. If not a tree, the subscriber may treat these changes as Create or Delete. Each notification is performed for a single item manipulation and the count of necessary notifications is calculated at the end of method call.