async-data.js

class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: undefined,
    };
  }

  componentWillMount() {
    fetch('http://api.openweathermap.org/data/2.5/weather?q=London&APPID=f1af35f060fb74c410aa54ab5ae9d943', { method: 'GET' })
      .then(response => response.json())
      .then((json) => {
        const data = json;
        this.setState({ data });
      });

  }


  render() {
    const datos = this.state.data;
    console.log('state', this.state);
    return datos ?
        (
          <div className="App">
          {
            datos.weather.map(item => item.description)
          }
          </div>
        ) : (<h1>Loading</h1>)
    
  }
}

/*React.render(
  <App />,
  document.getElementById('react_example')
);*/