I use `ReactDOM.unstable_renderSubtreeIntoContainer` to render a portal.

``` javascript
class Modal extends React.Component {

componentDidMount() {
    this.node = document.createElement('div');
    document.body.appendChild(this.node);
    this.renderPortal(this.props);
}

componentWillReceiveProps(nextProps) {
    this.renderPortal(nextProps);
}

componentWillUnmount() {
    ReactDOM.unmountComponentAtNode(this.node);
    document.body.removeChild(this.node);
}

renderPortal = (props) => {
    renderSubtreeIntoContainer(this, <ModalPortal {...props} />, this.node);
}

render() {
    return null;
  }
}
```

In my root component:

``` javascript
class App extends React.Component {
    static childContextTypes = {
        highlightColor: React.PropTypes.object
    }

    getChildContext() {
        return {
            highlightColor: this.props.highlightColor
        }
    }

    ...
}
```

The context of root component will be updated and passed to children if  `this.props.highlightColor` is changed. This is right.
I can access the correct context in the `<ModalPortal/>` component in the first render.
And after that the context passed to  `<ModalPortal/>` **does not change any more** when the context of root component changed.
But I can access the correct context in the `<Modal/>`  every render.

what's wrong with my code ?

var rootEl = getReactRootElementInContainer(container);
  if (rootEl) {
    var inst = ReactDOMComponentTree.getInstanceFromNode(rootEl);
    return !!(inst && inst._hostParent);
  }
}
function getHostRootInstanceInContainer(container) {
  var rootEl = getReactRootElementInContainer(container);
  var prevHostInstance =
    rootEl && ReactDOMComponentTree.getInstanceFromNode(rootEl);
  return (
    prevHostInstance && !prevHostInstance._hostParent ?
    prevHostInstance : null
  );
}
function getTopLevelWrapperInContainer(container) {
  var root = getHostRootInstanceInContainer(container);
  return root ? root._hostContainerInfo._topLevelWrapper : null;
}
/**
 * Temporary (?) hack so that we can store all top-level pending updates on
 * composites instead of having to worry about different types of components
 * here.
 */
var topLevelRootCounter = 1;