Is there a way to create a ComputedObservable in knockout that is computed from non-observable values and manually trigger the Notification?
Is there a way to create a ComputedObservable in knockout that is computed from non-observable values and manually trigger the Notification?
Essentially, a computed variable functions as a custom event handler for all observables within it.
Whenever an internal observable variable undergoes a change, a notify event is triggered and received by all listeners for further processing.
While the concept may seem straightforward, implementing it on plain JavaScript variables poses challenges. For more insights, check out Listening for variable changes in JavaScript or jQuery.
Should you choose to manually implement this, here are some basic hurdles you might encounter:
total variable requiring computation.My recommendation is to utilize computed (or pureComputed in KO3.2 and above) with observables. This approach streamlines your code significantly. The Knockout framework likely has addressed many of these challenges already, sparing you from reinventing the wheel and maintaining extensive undocumented code.
Included in this post is a Fiddle where I simulate the functionality of the textInput binding for numeric inputs. Notably, different handling methods for IE10, IE9, and pre-IE8 versions as well as special treatment for safari versions below 5 are showcased.
I completely agree with the previous response in suggesting to utilize ko.observable variables within your computed function. It seems unnecessary to use a computed function if its re-evaluation is not automated. In my opinion, it would be more effective to just create a simple function instead.
One potential solution could be to establish a placeholder observable that the computed function depends on. By calling valueHasMutated, you can trigger a re-evaluation:
var a = "A";
var b = "B";
var subscriptionObs = ko.observable();
var ab = ko.pureComputed(function() {
subscriptionObs();
return a + b;
});
ko.applyBindings({ab: ab });
b = "C";
subscriptionObs.valueHasMutated();<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>
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