Computed function not being invoked

Question

I have the following view-model

var viewModel = {
FLFSExamIsH: ko.observable(true),
FLFSROIEntryFieldDynPosBottom: ko.computed(function() {
    return this.FLFSExamIsH ? "flfs_ROIImagesRow3Pos" : "flfs_ROIImagesRow2Pos";
}),

};

in my html page I am binding a div as follows:

data-bind='css: FLFSROIEntryFieldDynPosBottom'

at some point in my code, I execute: viewModel.FLFSExamIsH(false);

But at all times (in the chrome debugger) viewModel.FLFSROIEntryFieldDynPosBottom() is always returning the 'flfs_ROIImagesRow2Pos', regardless of the update to the viewmodel: viewModel.FLFSExamIsH()

Setting a breakpoint on the computed function and updating that model variable doesn't re-evaluate the computed function either.

score 3 · Answer 1 · edited May 23 '17 at 10:25

3

You are missing parenthesis at

return this.FLFSExamIsH ? "flfs_ROIImagesRow3Pos" : "flfs_ROIImagesRow2Pos";
//                    ^^^ here, it should be this.FLFSExamIsH()

Plus since you are using not using a function to define your viewmodel, the computed should be added after (check this thread for more info):

var viewModel = {
    FLFSExamIsH: ko.observable(true),
};
viewModel.FLFSROIEntryFieldDynPosBottom = ko.computed(function() {
    return this.FLFSExamIsH() 
                 ? "flfs_ROIImagesRow3Pos" 
                 : "flfs_ROIImagesRow2Pos";
});

Demo

edited May 23 '17 at 10:25

Community

1
1

answered Jun 20 '14 at 14:12

GôTô

7,974
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this change causes an exception: 'Uncaught TypeError: undefined is not a function' – user3760423 Jun 20 '14 at 14:20
There was another problem, answer updated with example – GôTô Jun 20 '14 at 14:22
See my answer about that – Anders Jun 20 '14 at 14:22
@Anders yes indeed, I always keep [this thread](http://stackoverflow.com/questions/9589419/difference-between-knockout-view-models-declared-as-object-literals-vs-functions) in mind – GôTô Jun 20 '14 at 14:24

score 0 · Answer 2 · edited Jun 20 '14 at 17:09

0

You can't use the this keyword if you do not use a function constructor.

edited Jun 20 '14 at 17:09

PatrickSteele

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answered Jun 20 '14 at 14:14

Anders

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Computed function not being invoked

2 Answers2