It would be nice if you can check for connectivity status( online/offline ) of the user. So you can check if the user is online/offline by  polling the  navigator.onLine property.

Example:

(function () {
setInterval(function () {
var NetworkStatus = document.getElementById("status"),
isOnline = navigator.onLine;
if (isOnline) {
NetworkStatus.innerHTML = "Online";
NetworkStatus.className = "online";
}
else {
NetworkStatus.innerHTML = "Offline";
NetworkStatus.className = "offline";
}
}, 100);
})();
Add the element inside HTML5 body.
 
     <h1 id="status"></h1>

 
You can also add some css style for more effects.
 
.online {
  color: green;
 }
 
.offline {
         color: red;
}