Question

I am using RPNiemeyer kendo-knockout library. I have three view models that instantiate each other – FranchiseDetailsViewModel instantiates LanguageListViewModel which instantiates LanguageDetailsViewModel. The last viewmodel LanguageDetailsViewModel needs to have a reference to the parent FranchiseDetailsViewModel as its functionality depends on it.

html:

<div data-viewId="languageList" >
    <div id="languageList" data-bind="with: viewModel">
        <div id="languageListGrid" data-bind="kendoGrid: { data: languageViewModels, columns: [ 
                { 
                    field: 'Language', 
                    title: 'Language',
                    width: 50
                }

                ], 
            scrollable: false, sortable: true, pageable: false }" style="height: 380px">

        </div>
    </div>
</div>​

javascript

$(function () {

    var FranchiseDetailsViewModel = function () {
        var 
            self = this,
            initialize = function () {
                self.languagesInfoViewModel(new LanguageListViewModel(self));
                var parentViewModel = ({ viewModel: self.languagesInfoViewModel });
                var element = $('div[data-viewId="languageList"')[0];
                ko.applyBindings(parentViewModel, element);
            };

        FranchiseDetailsViewModel.prototype.languagesInfoViewModel = ko.observable();
        initialize();
    };

    var LanguageListViewModel = function (franchise) {
        var 
            self = this,
            initialize = function () {
                var languageViewModel = new LanguageDetailsViewModel(franchise);
                self.languageViewModels.push(languageViewModel);
            };
        LanguageListViewModel.prototype.languageViewModels = ko.observableArray([]);
        initialize();
    };

    var LanguageDetailsViewModel = function (franchise) {
        LanguageDetailsViewModel.prototype.Language = ko.observable("English");
       LanguageDetailsViewModel.prototype.franchise = franchise;
    };

    var initialize = new FranchiseDetailsViewModel();
});​

This reference to the parent view model causes some kind of a infinitive loop when the grid is binding to the source data. I am receiving Maximum call stack size exceeded error. I believe the error is in the kendo knockout library when binding to the source of the grid because if I remove the grid there are no errors on the knockout binding to the div on this line:

ko.applyBindings(parentViewModel, element);

Is this the real reason for this error and how can I fix this? I cannot remove the reference to the parent view model so my hope is to fix the kendo-knockout behavior when binding to the source data. Any help with working example will be greatly appreciated. Thanks.

http://jsfiddle.net/5Zkyg/43/

Update per Niemeyer`s comment:

I have a div with some properties bound to FranchiseDetailsViewModel. One of these properties represents a checkbox – name it isVisible. I have another div with properties bound to LanguageDetailsViewModel. Some of these properties are visible only if the checkbox of the FranchiseDetailsViewModel is checked. That is franchise.isVisible is true. This is the reason I need the franchise reference.

I am rather new to javascript and maybe I do not use the prototype property correctly. As I am instantiating my viewmodels with the new keyword I found that when assigning it to the prototype they become public and are visible in the markup so I can bind them. From your example I see that this.myProperty also makes the property public. I am not sure if there is a difference in my scenario.

I decided to use this.myData.parent = parent; as a solution to my problem. Thank You very much for your feedback.

Answer 1

Based on the comment above:

One option is to “hide” franchise, so that Knockout doesn’t recursively try to unwrap it. You can do this by making it a property of a function or observable (which is a function).

There are a few ways to do this:

var Child = function(parent) {

    //use parent directly from the argument passed to the constructor. available as part of the closure.
    this.myHandler = function() {
        parent.log();
    };        

    this.myData = ko.observable();

    //reference as a sub-observable. you can bind against myData.parent, but it will disappear when doing ko.toJS/ko.toJSON
    this.myData.parent = parent;


    //similar to sub-observable.  hide the actual value behind an empty function.  It will not be found when doing ko.toJS/ko.toJSON.
    this.parent = function() { };
    this.parent.value = parent;  
};

Example here: jsfiddle.net/rniemeyer/uSpZB.

Normally you would not want to put observables on the prototype, as they will be shared by all instances.