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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

const electron = require('electron');
const app = electron.app;
const BrowserWindow = electron.BrowserWindow;

let onlineStatusWindow;

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

online-status.html

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

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

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

There may be instances where you want 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

const electron = require('electron');
const app = electron.app;
const ipcMain = electron.ipcMain;
const BrowserWindow = electron.BrowserWindow;

let onlineStatusWindow;

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

ipcMain.on('online-status-changed', (event, status) => {
  console.log(status);
});

online-status.html

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

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

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