index.html

<!DOCTYPE html>
<html>
    <head>
	      <title>HTML5 Server Side Event Example in Go</title>
    </head>
    <body>

	      Yo {{.}}, here are some facinating messages about the
	      current time:<br>

	      <script type="text/javascript">
	       // Create a new HTML5 EventSource
         var hookTypes = ["nowPlaying", "playerTime", "queue"]

         for (let htype of hookTypes) {
            var source = new EventSource('/api/subscribe?hooktype='+htype);
            // Create a callback for when a new message is received.
            source.onmessage = function(e) {
                // Append the `data` attribute of the message to the DOM.
                document.body.innerHTML += htype + '  ' + e.data + '<br>';
                console.log(e.data)
            };
            source.onopen = () => { console.log('subscription open') }
            source.onclose = () => { console.log('subscription channel closed') }

            window.addEventListener('beforeUnload', () => {
                console.log('closing eventsource')
                source.close()
            })
         }
	      </script>
    </body>
</html>