index.html

<!DOCTYPE html>
<html>

<head>
    <title>Go WebSocket Test</title>
    <script>
        function log(message) {
            var logElement = document.getElementById("log");
            logElement.innerText += new Date().toISOString() + ": " + message + "\n";
        }

        function getWsUrl() {
            var loc = window.location, new_uri;
            if (loc.protocol === "https:") {
                new_uri = "wss:";
            } else {
                new_uri = "ws:";
            }
            new_uri += "//" + loc.host + "/websocket";
            return new_uri;
        }

        var ws;
        function connect() {
            log("Connecting");
            ws = new WebSocket(getWsUrl());
            ws.onopen = () => {
                log("Connected");
            };

            ws.onmessage = (event) => {
                log("Received: " + event.data);
            };

            ws.onclose = (event) => {
                log("Connection Closed, Reconnecting");
                setTimeout(connect, 1000);
            };

            ws.onerror = (error) => {
                log("Error, Closing");
                ws.close();
            };
        }

        window.onload = (event) => {
            // Connect button and input to send messages
            document.getElementById('send').onclick = (event) => {
                ws.send(document.getElementById("payload").value);
            }
            // Start a connection
            connect();
        };

    </script>
</head>

<body>
    <input id="payload" type="text" />
    <button id="send">Send</button>
    <pre id="log"></pre>
</body>

</html>