Using javascript for pinging a webapp to keep session open

Question

I\'m writing a greasemonkey script to keep session open on a webapp I use for work. Which javascript command would you use to create some feedback with the server and ensure the

Answer 1

Using some tips from Jesse's answer, here's the complete code.

You will need to update the @match param with your site's domain

// ==UserScript==
// @name         Auto session extender
// @namespace    http://obive.net/
// @version      0.2
// @description  Automatically extend server-side session
// @author       Charlie Hayes
// @match        http://obive.net/
// @grant   GM_getValue
// @grant   GM_setValue
// @noframes
// ==/UserScript==

(function() {
    'use strict';

    console.log('The session for this site will be extended automatically via userscript.');

    var minute = 60*1000;
    var refreshTime = 15 * minute;

    var iframe = document.createElement("iframe");
    iframe.style.width = 0;
    iframe.style.height=0;

    var loc = window.location;
    var src = loc.protocol +'//' + loc.host + loc.pathname;
    src += loc.search ? (loc.search + '&') : '?';
    src +=  'sessionextendercachebuster=';

    var reloadIframe = function(){
        var time = new Date().getTime();
        var lastRefresh = GM_getValue('lastRefresh');
        var timeSinceLastRefresh = time - lastRefresh;
        if (!lastRefresh || timeSinceLastRefresh > refreshTime - minute) {
            console.log('Auto-extending session');
            iframe.src = src + time;
            GM_setValue('lastRefresh',time);
            setTimeout(reloadIframe, refreshTime);

            setTimeout(function(){
                // Unload the iframe contents since it might be taking a lot of memory
                iframe.src='about:blank';
            },10000);
        }else{
            console.log('Another tab/window probably refreshed the session, waiting a bit longer');
            setTimeout(reloadIframe, refreshTime - timeSinceLastRefresh - minute);
        }
    };
    setTimeout(reloadIframe, refreshTime);
    document.body.appendChild(iframe);
})();