Binding handler 'value is not a function' knockoutJS

Question

I am stumped as to what is causing the problem here as this binding handler normally works fine (below)

ko.bindingHandlers.buttonGroupChecked = {
init: function(element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
    var value = valueAccessor();
    var newValueAccessor = function() {
        return {
            click: function() {
                value(allBindingsAccessor.get('val'));
            }
        };
    };
    ko.bindingHandlers.event.init(element, newValueAccessor,
            allBindingsAccessor, viewModel, bindingContext);
},
update: function(element, valueAccessor, allBindingsAccessor,
        viewModel, bindingContext) {
    if (allBindingsAccessor.get("val") === ko.unwrap(valueAccessor())) {
        helpers.activeClassSingle(element, "btn-info", "btn-success");
    }


}
};

I keep getting an error at line 7 value(allBindingsAccessor.get('val')); saying value is not a function?

The options are defined in my viewmodel as follows:-

self.yesNoOptions = [
    {val: 1, text: "Yes"},
    {val: 0, text: "No"}
];

And the corresponding HTML and binding is:-

<div class="btn-group btn-group-justified" data-bind="foreach: $root.yesNoOptions">
               <div class="btn btn-lg btn-info" data-bind="buttonGroupChecked: $root.currentVariation().variationAgreed, val: val, text: text"></div>
            </div>

Where $root.currentVariation().variationAgreed is an item that is currently selected and is an observable as part of the following object.

var observableWorkItemVariation = function(data){
var self = this;
data = data || {};
self.id = ko.observable(data.id || "");
self.orderWorkItemID = ko.observable(data.orderWorkItemID || "");
self.variationAgreed = ko.observable(data.variationAgreed || 0);
self.changeWorkBillable = ko.observable(data.changeWorkBillable || 1);
self.declareBillable = ko.observable(data.declareBillable || 0);

self.changeWorkBillable.subscribe(function(val){
   if(self.changeWorkBillable() == 0){
       self.declareBillable(0);
   } 
});

self.changeWorkPayable = ko.observable(data.changeWorkPayable || 1);
self.variationCode = ko.observable(data.variationCode || "");
}

It is correctly highlighting the selected item (No as it is defaulted to 0) but when I try to change it throws the error.

After you assign value, take a look at what it is: `console.debug("Value:", value);` Is it a function? — Roy J, Dec 08 '15 at 13:20

score 1 · Answer 1 · answered Dec 08 '15 at 19:25

It looks like value is out of scope when the click even is fired.

As it stands now you're defining value in the local scope of one function and you're then trying to access it later in the local scope of a different function.

I'd recommend using click binding directly on each div. Knockout will automatically pass you an instance of the ViewModel that was clicked, so you can use that inside of the click handler on the $root view model to figure out which button was clicked to make it active.

score 0 · Answer 2 · edited Dec 16 '15 at 10:16

Thank you for the suggestions, roy gave a useful comment.

The problem was that I was creating an object from another object and I was passing variables in as varName instead of varName() to get the value (or ko.toJS(object)) so it was passing the observable through as the value of the observable.

I struggled to spot this as if you do ko.toJS() on the viewModel in <pre> tags it will unwrap it and show the value as correct.

Hope that is clear for anyone experiencing the problem as well.

Binding handler 'value is not a function' knockoutJS

2 Answers2