Setting callback function for every observable for every ViewModel in knockout

Question

I am looking for a way to setup a callback function which will be invoked after every observable in every ViewModel.

Something similar to ajaxSend and ajaxComplete with jquery where a function will be called after each ajax call.

After looking for something like this in knockout, I found only few things: explicitly subscribing to observables and using computed observables. Neither of these things solves my problem, because I have a lot of ViewModels and therefore using this way I will be forced duplicate code in every ViewModel.

Is there a way in knockout to subscribe to the change of any observable in any model?

Ivan.Srb Ivan.Srb · Accepted Answer · 2014-03-30T17:12:02

You could try to do something like this:

1) Create function, that you want to be called when any observable in any viewModel changed (first parameter - value, second - event type, the same as in subscribe function third parameter):

function extendNotification(valueToNotify, event) {
    if (event != "beforeChange") {
        console.log("extend notification: " + valueToNotify);
    }
};

2) Create helper wrapper:

function beforeWrapper(fnBefore, fnOriginal) {
    return function () {
        fnBefore.apply(this, arguments);
        return fnOriginal.apply(this, arguments);
    };
};

3) And wrap ko.subscribable.fn.notifySubscribers function with your extender:

ko.subscribable.fn.notifySubscribers =
    beforeWrapper(extendNotification, ko.subscribable.fn.notifySubscribers);

May be it is not the best solution for your problem, but you could modify it if you want.
Demo Fiddle.

Setting callback function for every observable for every ViewModel in knockout

1 Answers