Start.js

let Start = React.createClass({

  childContextTypes: {
    user: React.PropTypes.object
  },

  getChildContext: function() {
    return this.state;
  },

  getInitialState: function() {
    return {user: null};
  },
  
  componentDidMount: function() {
    AppState.get('user').subscribe(user => {
      this.setState({user: user});
    });
  },

...

}