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Questions tagged [computed-observable]

A computed observable is a synchronously updated value based on other observables; if they change so does the computer observable, immediately. A term frequently used with Knockout.js.

A familiar computed observable would be a cell in a spreadsheet that contains the sum of a column. If any of the cells in the column change, the sum is immediately updated.

Reference: http://knockoutjs.com/documentation/computedObservables.html

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Force a computed property function to run

Given a computed property vm.checkedValueCount = ko.computed(function(){ var observables = getCurrentValues(); //an array of ko.observable[] return _.filter(observables, function(v) { return v() }).length; }); suppose getCurrentValues() can…
George Mauer
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Knockout: computed observable vs function

When using knockout, what is the advantage of using read-only computed observables rather than simple functions? Take the following viewmodel constructor and html snippet, for example: ​ var ViewModel = function(){ var self = this; …
Duncan
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How to create a computed observable array in Knockout

I would like to know how to create a computed observable array. In my view model, I have 2 observable arrays, and I would like to have a computed observable array that is simply both arrays combined. function ViewModel() { var self = this; …
Matt Mangold
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Why does my ko computed observable not update bound UI elements when its value changes?

I'm trying to wrap a cookie in a computed observable (which I'll later turn into a protectedObservable) and I'm having some problems with the computed observable. I was under the opinion that changes to the computed observable would be broadcast to…
Allen Rice
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Cannot write a value to a ko.computed unless you specify a 'write' option

I am trying to use computed properties in another computed properties and when i run code i am getting following error in console. Cannot write a value to a ko.computed unless you specify a 'write' option function AppViewModel() { var self =…
rahularyansharma
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Create a computed observable for formatted values for a bunch of variables

I have 3 observable variables in view-model, and want to output to formatted value. However, I don't want to write computed method for each of them since they are identical. What is the best way to reuse the code? Thanks. The code I am going to…
Gary Zi
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Knockout Observable Array with Sorting and Foreach Data-Binding

I have an array of objects that are hooked up into a knockout observable array. I needed to apply sorting to these arrays and I ran into some behavior that is a bit confusing. My first attempt involved applying the sort in the foreach…
ecozoic
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What is difference on ko.computed between deferEvaluation and extend({deferred: true})

I am little bit confused by behavior explanation of deferred calculation defined on ko.computed variable. Such computed variable might be defined with property deferEvaluation: true which should postpone evaluation to the moment when any other…
Jan Stanicek
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Why does a function behave like a computed?

Given the following HTML/JS (http://jsfiddle.net/mgs_jsfiddle/gUhm2/)

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mgs
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Prevent computed from collecting dependencies

Is there a good way to roughly achieve the following concept: var computed = ko.computed(function() { readSomeObservables(); //<-- if these change, notify computed ko.stopCollectingDependencies(); readSomeMoreObservables(); //<-- if…
Rex M
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knockout.js how to set selected option after confirm() cancelled within a ko.computed write

i have a selector element with options and default text: self._selected = ko.observable(); self.option = ko.computed({ read:function(){ return self._selected; }, write: function(data){ if(data){ …
GZH
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How to update an observable in a computed without triggering the computed?

I have a particular knockout observable that's used in many computed functions and it works exactly as it's supposed to. However on one of these computed functions I do NOT want it to trigger when the observable is updated. Code wise it would look…
Nathan
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Angular2 version of knockout's computed observable

I am currently working on porting some code that I have written from Knockout to Angular2. I really like the construct of computed observables in knockout which means the results of that function are only computed when the obeservables it depends…
Gabe O'Leary
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How to bind property on parent object with knockoutjs?

I'm developing a application with knockout.js framework. I have one viewmodel like that: var MyViewModel= { Id: ko.observable(), CountryCode: ko.observable(), NormalizedAddress: { COUNTRY_CODE: ko.computed(function ()…
ilMattion
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Wrapping localStorage in a writeable computed observable fails to bust the cache

I am new to KnockoutJS and am curious to see if this is possible. I am trying to wrap a local storage object in a writeable computed so that I can take advantage of the auto-binding goodness of KnockoutJS. However, the "read" operation doesn't…
Ryan Wheale
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