web.js

 <script>
        document.addEventListener("message", function (event) {
            let parsed = JSON.parse(event.data);
            if (parsed.type === "photo") {
                setPhoto(parsed.params);
            }
            if (parsed.type === "location") {
                setLocation(parsed.params);
            }
        });

        function setPhoto(params) {
            document.getElementById('img').setAttribute('src', 'data:image/png;base64,' + params.data);
        }

        function setLocation(params) {
            var myJSON = JSON.stringify(params);
            document.getElementById("demo").innerHTML = myJSON;
        }

    </script>
 <script>

        function myFunction() {
            window.postMessage("takePicture");

        }

    </script>