Currently if React is not loaded, ReactDOM shows this:

<img width="664" alt="screen shot 2017-08-08 at 3 36 52 pm" src="https://user-images.githubusercontent.com/810438/29077217-784c7624-7c4f-11e7-88bc-b055407523a9.png">

We should throw a nicer error message in the entry point I think.
});
      });
      
      
      return true;
    } else {
      if (__DEV__) {
        const rootEl = getReactRootElementInContainer(container);
        const hasNonRootReactChild = !!(rootEl &&
          ReactDOMComponentTree.getInstanceFromNode(rootEl));
        
        const isContainerReactRoot =
          container.nodeType === 1 &&
          isValidContainer(container.parentNode) &&
          !!container.parentNode._reactRootContainer;
        warning(
          !hasNonRootReactChild,
          "unmountComponentAtNode(): The node you're attempting to unmount " +
            'was rendered by React and is not a top-level container. %s',
          isContainerReactRoot
            ? 'You may have accidentally passed in a React root node instead ' +
                'of its container.'
            : 'Instead, have the parent component update its state and ' +
                'rerender in order to remove this component.',
        );
      }
      return false;
    }
  },
  findDOMNode: findDOMNode,