Can't access function component const inside function in react native

I declare in one of my function component App the constant audioRecorderPlayer. When I try to access it in the function onStartRecord I get the error Unhandled Rejection (TypeError): Cannot read property 'startRecorder' of undefined pointing to the line with audioRecorderPlayer.startRecorder() inside onStartRecord.

How do I have to implement audioRecorderPlayer in Typescript or ES6 to be able to access it in the onStartRecord method and all my functions within the App component?

const App: React.FC<Props> = (props) => {    // ...      // This is where I initialize the constant    const audioRecorderPlayer = new AudioRecorderPlayer();    // ...      const onStartRecord = () => {        // Here a valid object is printed in the console featuring startRecording()        console.log(audioRecorderPlayer);         // Here I try to access it        audioRecorderPlayer.startRecorder()            .then((result: string) => {                                   console.log(result);            });    };     // ...       return (<View style={styles.container}><ScrollView>                <Button title='Start Recording' onPress={() => onStartRecord()}/></ScrollView></View>    );}export default App;

Here is some modified code which seems to work. The Code above is not working.

class AudioRecorderPlayer {  startRecorder(): Promise < string > {    return new Promise((resolve) => {      resolve('Success!');    });  }}interface Props {  audioRecorderPlayer: AudioRecorderPlayer;}const App: React.FC < Props > = (props) => {  // This is where I initialize the constant  const audioRecorderPlayer = new AudioRecorderPlayer();  const onStartRecord = () => {    // Here I try to access it    console.log('Button clicked!')    audioRecorderPlayer.startRecorder()      .then((result: string) => {        console.log(result);      });  };  return ( <div><p> Press Button to trigger function </p> <button onClick = {() => onStartRecord()}>        Start Recording </button></div>  );}// Render itReactDOM.render( <  App title = "My App" / > ,  document.getElementById("react"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script><div id="react"></div>

EDIT:

I am using expo to run the app in my browser.