ko.pureComputed( options ) — Constructs a pure computed observable using an options object. This accepts the read, write, and owner options described above. Using a computed observable. A computed observable provides the following functions: dispose() — Manually disposes the computed observable, clearing all subscriptions to dependencies. This function is useful if you.
Since this computed is declared to be pure (i.e.
its evaluator does not directly modify other objects or state), Knockout can more efficiently manage its re-evaluation and memory use. Knockout will automatically suspend or release it if no other code has an active dependency on it. Pure computeds were introduced in Knockout 3.2.0.
If you create a computed observable in a custom binding, rather than using a custom disposal callback, you can set the computed to dispose automatically when the node is removed. When constructing the computed observable, provide the node using the disposeWhenNodeIsRemoved option: ko.computed ( {. read: function () {.
I take care of disposing every manual subscription and computed /pureComputed with dispose (), but I am afraid that something of the manual subscription remains. In the subscription object, I can find inside a da() object, which is the observable subscribed. … 0 >>> x = ko . computed (function { y() }) >>> y.getSubscriptionsCount() 1 >>> x. dispose …
#483 – Modify ko.computed to dispose itself if it has no dependencies… The computed is then flagged as inactive and does not need to be tracked. Modify templating and arrayToDomNodeChildren to only store the computed if it’s active.
Disposing a computed observable will make it clean up all of its subscriptions. So, while you could still write to it, the read function will not run again. Disposal does not null out the computed , it is meant to make sure that there are no lingering subscriptions.
A true-ish result will trigger disposal of the computed observable. disposeWhenNodeIsRemoved — Optional. If given, disposal of the com puted observable will be triggered when the specified DOM node is removed by KO. This feature is used to dispose computed observables used in bindings when nodes are removed by the template and control-flow bindings.
The dispose callback would remove the node from the array, and if the array was empty, finally dispose the computed . I then realized that other areas of Knockout could use this same functionality (templates specifically) and so generalized it within ko . computed .
