Simple JS which polls a given script eveny X seconds, using an image rather than Ajax-style request.

pinger.js

Pinger = function(opts) { for (var o in opts) { this.config[o] = opts[o]; } }
Pinger.prototype = {
	running: false,
	config: {
		host     : document.location.host,
		secure   : (document.location.protocol == "https:"),
		script   : '',
		interval : 300 // interval time in seconds
	},
	start: function() { this.running = true; this.schedule(); },
	stop: function() { this.running = false; },
	schedule: function() { window.setTimeout(this.poll(), this.config.interval * 1000); },
	poll: function() { var scope = this; return function() { return scope.ping.apply(scope); } },
	ping: function() {
		if (!this.running) { return; }
		new Image(1,1).src = "http" + (this.config.secure ? 's' : '') + "://"
		  + this.config.host + this.config.script + "?" + Math.floor(Math.random()*9999999);
		this.schedule();
	}
};

/**
 * Usage:
 * var p = new.Pinger({host: 'mydomain.com', script: '/path/to/script.xxx', interval: 60});
 * p.start();
 * p.stop();
 */