code: function (object, property, value) {
          if (object[OBSERVER_PROPERTY]) {
              var existed = ownProperty.call(object, property), oldVal = object[property];
              delete object[property];
  
              if (existed) {
                  var chgset=[changeDesc(object, property, object[property], oldVal, "deleted")];
                  callObservers(object, chgset);
              }
          } else {
              delete object[property];
          }
      }
docs: Delete a property in a JSON object and automatically notifies all observers of the change