title: Video mediaDevices.getUserMedia zoom is not working in iOS
body: <p>I'm implementing <a href="https://github.com/zxing-js/library" rel="nofollow noreferrer">zxing-js</a> to scan QR Code.
  My task is to enable zoom while using the camera. It works well in Chrome on Android devices, but when I try to use it on iOS it doesn't work.</p>
  
  <p>Below is my code:</p>
  
  <pre><code>navigator.mediaDevices.getUserMedia(environment).then(async mediaStream =&gt; {
      document.querySelector('video').srcObject = mediaStream;
  
      await sleep(1000);
  
      const track = mediaStream.getVideoTracks()[0];
      const capabilities = track.getCapabilities();
      const settings = track.getSettings();
  
      const input = document.querySelector('input[type="range"]');
  
      // Check whether zoom is supported or not.
      if (!('zoom' in capabilities)) {
          return $(log).html('Zoom is not supported by ' + track.label);
      }
  
      // Map zoom to a slider element.
      input.min = capabilities.zoom.min;
      input.max = capabilities.zoom.max;
      input.step = capabilities.zoom.step;
      input.value = settings.zoom;
      input.oninput = function(event) {
          track.applyConstraints({advanced: [ {zoom: event.target.value} ]});
      }
      input.hidden = false;
  });
  </code></pre>
  
  <p>When I check inside the <code>capabilities</code> using iOS device, the <code>zoom</code> attribute is not on the list. Any ideas on how can I solve this problem?</p>
  
  <p>Thank you so much!</p>