# Online/Offline Event Detection

Online and offline event detection can be implemented in the renderer process
using standard HTML5 APIs, as shown in the following example.

_main.js_

```javascript
var app = require('app');
var BrowserWindow = require('browser-window');
var onlineStatusWindow;

app.on('ready', function() {
  onlineStatusWindow = new BrowserWindow({ width: 0, height: 0, show: false });
  onlineStatusWindow.loadUrl('file://' + __dirname + '/online-status.html');
});
```

_online-status.html_

```html
<!DOCTYPE html>
<html>
  <body>
    <script>
      var alertOnlineStatus = function() {
        window.alert(navigator.onLine ? 'online' : 'offline');
      };

      window.addEventListener('online',  alertOnlineStatus);
      window.addEventListener('offline',  alertOnlineStatus);

      alertOnlineStatus();
    </script>
  </body>
</html>
```

There may be instances where one wants to respond to these events in the
main process as well.  The main process however does not have a
`navigator` object and thus cannot detect these events directly.  Using
Atom-shell's inter-process communication utilities, the events can be forwarded
to the main process and handled as needed, as shown in the following example.

_main.js_

```javascript
var app = require('app');
var ipc = require('ipc');
var BrowserWindow = require('browser-window');
var onlineStatusWindow;

app.on('ready', function() {
  onlineStatusWindow = new BrowserWindow({ width: 0, height: 0, show: false });
  onlineStatusWindow.loadUrl('file://' + __dirname + '/online-status.html');
});

ipc.on('online-status-changed', function(event, status) {
  console.log(status);
});
```

_online-status.html_

```html
<!DOCTYPE html>
<html>
  <body>
    <script>
      var ipc = require('ipc');
      var updateOnlineStatus = function() {
        ipc.send('online-status-changed', navigator.onLine ? 'online' : 'offline');
      };

      window.addEventListener('online',  updateOnlineStatus);
      window.addEventListener('offline',  updateOnlineStatus);

      updateOnlineStatus();
    </script>
  </body>
</html>
```
