Question

I have a ViewModel that holds a subclass, and I want to be notified when one of the property in the subclass is modified, something like this:

var Person = function(){
  this.name = ko.observable("john doe");
  this.age = ko.observable(45);
};

var ViewModel = function() {
  this.Owner = ko.observable(new Person());

  this.Owner().subscribe(function(){
     alert("Someone updated owner");
  });    
};

var vm = new ViewModel();
vm.Owner().age(34);
​

But the above code doesn’t work…

Answer 1

You can try this:

var ViewModel = function() {
    var self = this;
    self.Owner = ko.observable(new Person());

    self.test = ko.computed(function(){
        ko.toJS(self.Owner);
    });

    self.test.subscribe(function() {
        alert("Someone updated owner");
    });
};

Here is working fiddle: http://jsfiddle.net/vyshniakov/hpKZj/

If you want to implement something like isDirty flag read the following article: http://www.knockmeout.net/2011/05/creating-smart-dirty-flag-in-knockoutjs.html