detect change on navigator.online

Question

How can I detect if the navigator changed your state to online/offline?

something like:

var oldState = navigator.onLine; 
window.navigator.onlinechange = function(evnt,newState) { 
         alert('your changed from' + oldState + ' to' + newState + 'state');
}

Answer 1

Something like this (not every browser supports these events, currently only IE 8,9 and FF > 3 support these events):

var el = document.body;
if (el.addEventListener) {
   el.addEventListener("online", function () {
     alert("online");}, true);
   el.addEventListener("offline", function () {
     alert("offline");}, true);
}
else if (el.attachEvent) {
   el.attachEvent("ononline", function () {
     alert("online");});
   el.attachEvent("onoffline", function () {
     alert("offline");});
}
else {
   el.ononline = function () {
     alert("online");};
   el.onoffline = function () {
     alert("offline");};
}

The browser support varies, check this out: http://help.dottoro.com/ljnasgpu.php

Answer 2

With the help of classes on body and this code you can find

window.ononline = function() {
    alert('You are now online');
}

window.onoffline = function() {
    alert('You are now offline');
}

Answer 3

If it needs to be more cross browser compatible you have to poll the navigator.onLine property.

var status = document.getElementById('status')

setInterval(function () {
  status.innerHTML = navigator.onLine ? 'online' : 'offline';  
}, 250);

Demo: http://html5demos.com/nav-online