qrcode.html

<html>
  <head>
    <title>QRCode Reader</title>
    <script type="text/javascript" src="{{
        url_for('static', filename='instascan.min.js')}}"></script>	
	 <style>
      .text{
        resize: none;
      }
    </style>
  </head>
  <body>
    <video id="preview"></video>
	<textarea disabled class="text" id='qr'>QRcode info</textarea>
    <script>
        let scanner = new Instascan.Scanner(
            {
                video: document.getElementById('preview')
            }
        );
		
		Instascan.Camera.getCameras().then(cameras => 
        {
            if(cameras.length > 0){
                scanner.start(cameras[0]);
            } else {
                console.error("No Camera Found");
            }
        });
		
        scanner.addListener('scan', function(content) {
			document.getElementById('qr').value = content;
        });
    </script>

 </body>
</html>