navigator.onLine is not a good way to test if the client is connected to the internet in an html5 offline application

navigator.onLine.alternative.js

var serverReachable = function() {
	// IE vs. standard XHR creation
	var x = new(window.ActiveXObject || XMLHttpRequest)("Microsoft.XMLHTTP"),
		s;
	x.open(
	// requesting the headers is faster, and just enough
	"HEAD",
	// append a random string to the current hostname,
	// to make sure we're not hitting the cache
	"//" + window.location.hostname + "/?rand=" + Math.random(),
	// make a synchronous request
	false);
	try {
		x.send();
		s = x.status;
		// Make sure the server is reachable
		return (s >= 200 && s < 300 || s === 304);
		// catch network & other problems
	} catch (e) {
		return false;
	}
}