Since Knockout 3.0 there has been an arrayChange event that can be attached to an observable or observableArray.

One subscribes to changes as follows:

obsArray.subscribe(fn, thisArg, "arrayChange");

The main advantages of subscribing to changes:

• Performance is O(1) in most cases, i.e., there’s basically no performance implication at all, because for straightforward operations, (push, splice, etc.) KO supplies the change log without running any diff algorithm. KO now only falls back on the diff algorithm if you’ve made an arbitrary change without using a typical array mutation function.

• The change log is filtered down just to give you the items that actually changed.

The observableArray has array tracking enabled at construction, but you can extend any other subscribable (i.e. ko.observable and ko.computed) by extending it as follows:

trackable = ko.observable().extend({trackArrayChanges: true});