const [result, setResult] = useState('');
const [facingMode, setFacingMode] = useState('environment');
 
return (
  <div className="App">
    <h1>Code Scanner</h1>
    <div>Result: {result}</div>
    <div>
      <button onClick={() => setResult('')}>reset</button>
    </div>
    <div>
      <button
        onClick={() =>
          setFacingMode(facingMode === 'environment' ? 'user' : 'environment')
        }
      >
        current camera: {facingMode} switch camera
      </button>
    </div>
    <CodeScanner
      onResult={res => setResult(res.map(({ value }) => value).join(', '))}
      onError={setResult}
      facingMode={facingMode}
    />
  </div>
);