index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" http-equiv="Content-Type" content="text/html; charset=utf-8">
    <script type="text/javascript" src="/qrcode.js"></script>
    <script type="text/javascript" src="/html5-qrcode.js"></script>
    <title> Bitcore Address & QR Code Generator </title>
    <style type="text/css" media="screen">
        body { text-align:center; }
    </style>
</head>

<body>
    <header>
        <h1>Bitcore Address</h1>
    </header>
    <form action="/BTC" method="GET">
        <fieldset>
            <button type="submit">Click me to generate address</button>
            &nbsp;&nbsp;&nbsp;&nbsp;
            <label id="address"></label>
        </fieldset>
    </form>
    <br><br><br>

    <script>
        var parameters = location.search.substring(1).split("&");
        var temp = parameters[0].split("=");
        var innerHTML = unescape(temp[1]);
        var disableFlag = false;
        if(innerHTML == 'undefined')   {
            disableFlag = true;
        }else   {
            document.getElementById("address").innerHTML = innerHTML;
        }
    </script>

    <div id="qrcode"></div>

    <script type="text/javascript">
        function updateQRCode(text) {
            var element = document.getElementById("qrcode");
            var bodyElement = document.body;
            if (element.lastChild) {
                element.replaceChild(showQRCode(text), element.lastChild);
            }
            else {
                element.appendChild(showQRCode(text));
            }

        }
        var x = document.getElementById("qrcode");
        if(!disableFlag)    {
            updateQRCode(document.getElementById("address").innerHTML);
        }
    </script>
</body>