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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

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

<!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 Electron'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

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

<!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>