app.js

import environment from './createRelayEnvironment'
// ...
const root = <QueryRenderer
  environment={environment}
  query={graphql`
    query appQuery {
      viewer {
        ...TodoApp_viewer
      }
    }
  `}
  render={({error, props}) => {
    if (props) {
      return <TodoApp viewer={props.viewer} />
    } else {
      return <div>Loading</div>
    }
  }}
/>