Question

I am learning knokcout.js

I was using the example in http://www.knockmeout.net/2011/04/utility-functions-in-knockoutjs.html, which is working fine.

I added the following to the javascript there.

viewModel.breads = ko.dependentObservable(function() {

        return ko.utils.arrayFilter(this.items(), function(item) {
            return item.category()=='Bread';
        });

}, viewModel);

It was working.

Then I added the follwing

viewModel.breadsLength = ko.dependentObservable(function() {

        var filtered_array= ko.utils.arrayFilter(this.items(), function(item) {
            return item.category()=='Bread';
        });

        return filtered_array().length;

}, viewModel);

This makes the whole javascript fail. I tried filtered_array.length(), filtered_array().length(), this.breads.length() etc. I was not able to get it to work.

Displaying array length by data-bind="text: breads().length" works only once and does not seem to update whenever I use a new json.

Answer 1

In this case, you would just want to do: filtered_array.length. The result of ko.utils.arrayFilter is a normal array and you would be checking the length property of it (which is not an observable).