HTML5 server sent events with ASP.net Web Forms when any updates happen in table

Question

I want to implement HTML5 Server Sent Event feature with ASP.NET Web Forms with Web Service.

My client code is

$(document).ready(function () {
            initialize();
        });
        function initialize() {
            if (window.EventSource == undefined) {
                document.getElementById('OutputDiv').innerHTML = "Your browser doesn't support Server Side Events.";
                return;
            }
            var source = new EventSource("WebSercvice.asmx");
            source.onopen = function (event) {
                document.getElementById('OutputDiv').innerHTML += 'Connection Opened.<br>';
            };
            source.onerror = function (event) {
                if (event.eventPhase == EventSource.CLOSED) {
                    document.getElementById('OutputDiv').innerHTML += 'Connection Closed.<br>';
                }
            };
            source.onmessage = function (event) {
                document.getElementById('OutputDiv').innerHTML += event.data + '<br>';
            };

and Server side code is

[WebMethod]
    public void HelloWorld() {
        DateTime startDate = DateTime.Now;
        HttpContext.Current.Response.ContentType = "text/event-stream";
        while (startDate.AddMinutes(1) > DateTime.Now)
        {
            HttpContext.Current.Response.Write(string.Format("data: {0}\n\n", startDate));
            HttpContext.Current.Response.Flush();
            System.Threading.Thread.Sleep(1000);
        }
    }

But it is not able to call the service method.