I'm having a problem with adding a knockout extender to observables after they have been created. In the following example the extender is run on foo every time the value changes as expected but only once, when first called, for bar.

var viewModel = function(){
    var self = this;

    self.foo = ko.observable(1).extend({ numeric: 1 });

    self.bar = ko.observable(1);

    self.bar.extend({ numeric: 1 });
};

Essentially I am mapping a large JSON object and would like to add extenders after the mapping has occurred to some of the properties. Is there a simple way to do this?

Below is a jsfiddle showing the problem:

/

I'm having a problem with adding a knockout extender to observables after they have been created. In the following example the extender is run on foo every time the value changes as expected but only once, when first called, for bar.

var viewModel = function(){
    var self = this;

    self.foo = ko.observable(1).extend({ numeric: 1 });

    self.bar = ko.observable(1);

    self.bar.extend({ numeric: 1 });
};

Essentially I am mapping a large JSON object and would like to add extenders after the mapping has occurred to some of the properties. Is there a simple way to do this?

Below is a jsfiddle showing the problem:

http://jsfiddle/LgxTn/

• javascript
• knockout.js

1 Answer 1

The problem you have is that the extender is creating a new observable (based on the observable it's extending). And that new observable is not being used in your second call to extend.

To fix this (without changing the code of the extender) you can assign the response from calling extend into the same property it's called.

In other words, add self.bar = in front of your last line in order to have this:

self.bar = self.bar.extend({ numeric: 1 });