title: AsyncStorage returns unexpected error
body: <p>Please forgive me if this question is caused by syntax error or of the sort, I'm new to React-Native and there is still many to learn.</p>
  
  <p>I followed the docs and tried out AsyncStorage but it returns an error.</p>
  
  <pre><code>class iCare extends Component {
  
  constructor(props) {
  super(props);
  
  async getUserStatus(key){
    try{
      var value = await AsyncStorage.getItem(key);
      if (value == null || value == 0){
        console.log('No loggedIn key yet.');
        loggedIn: false;
      } else {
        console.log('loggedIn key existed');
        loggedIn: true;
      }
    }catch(error){
      console.log('caught error' + error);
    }
  }
  }
  </code></pre>
  
  <p>The error says something is wrong with <strong>AsyncStorage</strong>, but why?
  <a href="https://i.stack.imgur.com/FUI5E.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FUI5E.jpg" alt="Screenshot"></a></p>
  
  <p>Just for the knowledge, is it wise to do AsyncOperation in a constructor method?</p>