title: How to remove event listener for react-native-tts async function in React Native
body: <p>I have tried the following code to remove event listener in the <code>componentWillUnmount</code> lifecycle method:</p>
  
  <pre><code>class MyComponent extends Component {
    constructor(props) {
      super(props);
      this.subscription = Tts.addEventListener('tts-finish', this._startRecognition.bind(this));
    }
  
    componentWillMount() {
      Tts.speak('Welcome to Hello World');
    }
  
    _startRecognition() {
      console.log('==================== recognizing text that was spoken ====================');
    }
  
    componentWillUnmount() {
      Tts.removeEventListener('tts-finish');
    }
  }
  </code></pre>
  
  <p>When I open this component again, it will fire up the <code>_startRecognition</code> method. Is there an elegant way to removing event listener. Any help would be greatly appreciated.</p>