title: Access ViewModel Property in ko.utils.extend
body: <p>I have a viewModel.</p>
  
  <pre><code>  var Vm = function() {
          var self = this;
          self.severityList = ko.observableArray(ko.utils.parseJson('@Html.Raw(jsonData)'));
          self.deactivateSeverityLevel.bind(this);
      };
      ko.utils.extend(Vm.prototype, {
          deactivateSeverityLevel: function(item) {
  
          }
      });
  </code></pre>
  
  <p>I need to access the severityList inside the ko.utils.extend.
  I try to add Vm.severityList inside the .extend but it's not working..</p>