Check if there is an internet connection

Question

How to check if there is an internet connection in Javascript? I have searched in Google but I have not found a good solution for my problem.

I have already got two eventhandler:

document.body.addEventListener("offline", function () {
    //alert("offline")
    masterViewModel.online(false)
}, false);
document.body.addEventListener("online", function () {
    //alert("online")
    masterViewModel.online(true);
}, false);

But how to check in the "onload"-function if I am online?

Well, nope, you can open page from local server or even from file system. The only thing I can suggest is to create lightweight ajax request and timeout counter. If timeout fired, connection probably broken. — Tommi, Apr 16 '13 at 11:17
Check http://stackoverflow.com/questions/2384167/check-if-internet-connection-exists-with-javascript — niksvp, Apr 16 '13 at 11:21

score 28 · Accepted Answer · answered Apr 16 '13 at 11:20

28

In HTML5, according to the specs:

var online = navigator.onLine;

answered Apr 16 '13 at 11:20

UltraInstinct

43,308
12
81
104

score 3 · Answer 2 · answered Apr 16 '13 at 11:23

3

Hi You can do like this:

var connectionMessage = "internet connection";
var noConnectionMessage = "No internet connection.";
window.onload = checkInternetConnection;
function checkInternetConnection() {
  var isOnLine = navigator.onLine;
   if (isOnLine) {
      alert(connectionMessage);
   } else {
     alert(noConnectionMessage);
   }
}

answered Apr 16 '13 at 11:23

ravisolanki07

637
3
13

1

I love how you change both messages just to correct a grammar problem xD – Benedict Lewis Apr 16 '13 at 11:27

Parth Chavda · Answer 3 · 2015-11-19T10:40:10.267

var online = navigator.onLine; is doesn't work every time.Sometime your connection is enabled but you can not fetch data from internet or not access a site even if you are online...so that time online return true because you are online.that time "navigator.onLine" is not usable.

" You could be getting false positives, such as in cases where the computer is running a virtualization software that has virtual ethernet adapters that are always "connected." Therefore, if you really want to determine the online status of the browser, you should develop additional means for checking. To learn more, see the HTML5 Rocks article, " check this article

you must use ajax request to check....

score 0 · Answer 4 · answered Apr 04 '17 at 17:38

0

Why not just make an ajax call to a well-known address, say StackOverflow. If you don't get 404, you are online.

answered Apr 04 '17 at 17:38

user1556718

91
1
9

1

If there is no internet or the server is down, there is no 404. – Pedro Casagrande Nov 09 '17 at 12:58
1

404 is an actual response from a server, thus, you need to be online to get a 404. – tomacco Feb 22 '18 at 08:58
A 4xx response comes from the server, you won't get them when having no connection. You could also get a false positive if the site you're targeting is down. – Enric A. Jul 29 '20 at 09:52

Check if there is an internet connection

4 Answers4