Question

I have several knockout models, that I use on my website. Let’s say for a given model I have a property

function modelA {
    this.doSomething = function () { ... };
}

Now i want to use the doSomething() function in a different model. I would like to do this, such that I am not obligated to rewrite doSomething() in every single model that needs it. Ideally i would like it if this function becomes available as soon as ko.applyBindings(new modelX()) is called.

I know that i can have the functions inherit from a prototype, but that also leads repeated code in every single model. Is there a way to alter knockout.js to inject this property into all model objects?

EDIT:

In case there’s a different approach that would achieve my desired goal, i’ll elaborate on that desired goal. We use knockout-validation.js which allows me to call isValid() on every property in a model that has been extended with validation rules. I want to append a function to every model that will inspect the other properties in the model, and call isValid() on them. That way i can write a generic validation function that can be used with every model, without having to explicitly add it to the model.

Answer 1

You can add a custom function onto knockout’s core datatypes. Alternatively you could look at extenders, and inside the extension you could add the function to an observable. Note, however, that both of these techniques address cross-cutting concerns at the “observable” level, not at the ViewModel level.

I would be curious to understand what doSomething is doing. Assuming that it has to access some observable(s) inside the ViewModel you should be able to reframe the problem so that the behaviour is attached to an observable.