ajaxpoll.js

/*
    Extended Ajax JavaScript functions used by AjaxPage.

    Implements a periodic polling mechanism to prevent server timeouts
    and to allow pushing commands from the server to the client.

    Written by John Dickinson based on ideas from
    Apple Developer Connection and DivMod Nevow.
    Some changes made by Christoph Zwerschke.
*/

var dying = false;
var poll_requester = getRequester();

function openPollConnection()
{
    if (poll_requester)
    {
        var req = poll_requester;
        req.onreadystatechange = function() {
            var wait = 3 + Math.random() * 5; // 3 - 8 seconds
            if (req.readyState == 4) {
                if (req.status == 200) {
                    try {
                        eval(req.responseText);
                        req.abort();
                    } catch(e) { } // ignore errors
                    if (!dying) {
                        // reopen the response connection after a wait period
                        setTimeout("openPollConnection()", wait*1000);
                    }
                }
            }
        }
        var url = request_url + 'Poll&_req_=' + ++request_id;
        req.open("GET", url, true);
        req.send(null);
    }
}

function shutdown()
{
    if (poll_requester) {
        poll_requester.abort();
    }
    dying = true;
}

if (window.addEventListener)
    window.addEventListener("beforeunload", shutdown, false);
else if (window.attachEvent)  // MSIE
    window.attachEvent("onbeforeunload", shutdown);

// Open initial connection back to server:
openPollConnection();