const {observable, asMap} = mobx;

const {observer} = mobxReact;

​

@observer

class App extends React.Component {

  @observable book = asMap({

    name: 'The Secret', 

    language: 'English'

  });

  addYear = () => {

    this.book.set('year', '2006');

  };

  render() {

     const year = this.book.get('year');

     return <div> 

       <div>Name: {this.book.get('name')}</div>

       <div>Language: {this.book.get('language')}</div>

       {year ? <div>Published Year: {year}</div> : null}

       <button onClick={this.addYear}> Add Year </button>

     </div>;

  }

}

​

ReactDOM.render(

  <App />,

  document.getElementById('app')

);