title: facingMode property not working in react-qr-scanner in react js
body: <p>In one of my react js application, I need to integrate QR scanner.
  I am using <strong>react-qr-scanner</strong> npm library (version 1.0.0-alpha.7 to be specific).</p>
  <p>The issues I am facing is:</p>
  <ol>
  <li>Default front camera is only working and I am not able to use rear camera for scanning.
  I have used property: <code>facingMode=&quot;rear&quot;</code> but this is not making any difference.</li>
  <li>I am not able to list available camera options to select from. Any help in this would be appreciated.</li>
  </ol>
  <p>Below is example code snippet:</p>
  <pre><code>          &lt;QrReader
              facingMode=&quot;rear&quot;
              delay={500}
              style={styles.previewStyle}
              onError={handleError}
              onScan={handleScan}
            /&gt;
  </code></pre>
  <p>Library reference URL is: <a href="https://www.npmjs.com/package/react-qr-scanner" rel="nofollow noreferrer">https://www.npmjs.com/package/react-qr-scanner</a></p>
  <p>Thanks in advance for any help and suggestions!</p>