JavaScript初心者がES2015をReactとかに適用する時に色々ハマったことのちょっとしたまとめ ref: http://qiita.com/takuan_osho/items/c938ef0d4a7ed11a159f

sample.js

var MyComponent = React.createClass({
  getInitialState() {
    return {
      newTodo: ""
    };
  }
});

sample1.js

class MyComponent extends React.Component {
  constructor() {
    super();
    this.state = {newTodo: ""};
  }
}

sample3.js

class TodoFooter extends Component {
  constructor {
    super();
    this.handleClearCompleted = this.handleClearCompleted.bind(this);
  }
}