title: abort fetch when component unmount
body: <p>how could I cancel fetch operation when component go away (unmount)</p>
  
  <p><strong>example</strong> :  user open this screen and go back before fetch complete</p>
  
  <p>here is what I have done</p>
  
  <pre><code>export default class LecturesScreen extends React.Component
  {
        constructor(props){
          super(props);
          this.state = {lectures : [] , loadingNow : true}
      }
  
      componentDidMount(){
          this.loadLectures();
      }
  
      loadLectures = () =&gt;{
          fetch(Link.api.lecture.newest , {method : 'POST'})
              .then((response) =&gt;
              {
                  this.setState({lectures : response , loadingNow: false});
              })
              .catch((error)=&gt;
              {
                  console.log(error);
              });
      };
  
      render(){
          return (
              &lt;View&gt;
  
                  &lt;List dataArray={this.state.lectures}
                        renderRow={(item) =&gt; &lt;LectureListItem title={item.Title}/&gt;}
                  /&gt;
  
              &lt;/View&gt;
          );
      }
  }
  </code></pre>