anchor.diff:    incrementChildValue(_) {
       ref("childRef").incrementValue();
     }
  +
  +  // Callback refs
  +  JsObject _inputCallbackRef;
  +  _ChildComponent _childCallbackRef;
  +  showInputCallbackRefValue(_) {
  +    var input = react.findDOMNode(_inputCallbackRef);
  +    print(input.value);
  +  }
  +  showChildCallbackRefValue(_) {
  +    print(_childCallbackRef.somevalue);
  +  }
  +  incrementChildCallbackRefValue(_) {
  +    _childCallbackRef.incrementValue();
  +  }
  +
     render() =>
       react.div({},[
  +      react.h1({}, "String refs"),
  +      react.h4({}, "<input>"),
         react.input({"ref": "inputRef"}),
  -      react.button({"onClick": showInputValue}, "print input element value"),
  +      react.button({"onClick": showInputValue}, "Print input element value"),
  +      react.h4({}, "ChildComponent"),
         ChildComponent({"ref": "childRef"}),
  -      react.button({"onClick": showChildValue}, "Show child value"),
  -      react.button({"onClick": incrementChildValue}, "Show child value"),
  +      react.button({"onClick": showChildValue}, "Print child value"),
  +      react.button({"onClick": incrementChildValue}, "Increment child value"),
   
  +      react.h1({}, "Callback refs"),
  +      react.h4({}, "<input>"),
  +      react.input({"ref": (instance) => _inputCallbackRef = instance}),
  +      react.button({"onClick": showInputCallbackRefValue}, "Print input element value"),
  +      react.h4({}, "ChildComponent"),
  +      ChildComponent({"ref": (instance) => _childCallbackRef = instance}),
  +      react.button({"onClick": showChildCallbackRefValue}, "Print child value"),
  +      react.button({"onClick": incrementChildCallbackRefValue}, "Increment child value"),
       ]);
   }
   
  
positive.code: import "package:react/react.dart" as react;
  import "package:react/react_client.dart";
  import "dart:html";
  
  
  var ChildComponent = react.registerComponent(() => new _ChildComponent());
  class _ChildComponent extends react.Component {
  
negative.code: 
  var ParrentComponent = react.registerComponent(() => new _ParrentComponent());
  class _ParrentComponent extends react.Component {
    // String refs
    showInputValue(_) {
      var input = react.findDOMNode(ref('inputRef')) as InputElement;
      print(input.value);
  