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# Online/Offline Event Detection
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-[Online and offline event](https://developer.mozilla.org/en-US/docs/Online_and_offline_events) detection can be implemented in the renderer process using the [`navigator.onLine`](http://html5index.org/Offline%20-%20NavigatorOnLine.html) attribute, part of standard HTML5 API.
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-The `navigator.onLine` attribute returns `false` if any network requests are guaranteed to fail i.e. definitely offline (disconnected from the network). It returns `true` in all other cases.
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-Since all other conditions return `true`, one has to be mindful of getting false positives, as we cannot assume `true` value necessarily means that Electron can access the internet. Such as in cases where the computer is running a virtualization software that has virtual ethernet adapters that are always “connected.”
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-Therefore, if you really want to determine the internet access status of Electron,
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-you should develop additional means for checking.
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+## Overview
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-Example:
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+[Online and offline event](https://developer.mozilla.org/en-US/docs/Online_and_offline_events)
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+detection can be implemented in the Renderer process using the
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+[`navigator.onLine`](http://html5index.org/Offline%20-%20NavigatorOnLine.html)
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+attribute, part of standard HTML5 API.
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-_main.js_
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+The `navigator.onLine` attribute returns:
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+* `false` if all network requests are guaranteed to fail (e.g. when disconnected from the network).
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+* `true` in all other cases.
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+
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+Since many cases return `true`, you should treat with care situations of
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+getting false positives, as we cannot always assume that `true` value means
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+that Electron can access the Internet. For example, in cases when the computer
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+is running a virtualization software that has virtual Ethernet adapters in "always
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+connected" state. Therefore, if you want to determine the Internet access
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+status of Electron, you should develop additional means for this check.
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+
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+## Example
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+
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+### Event detection in the Renderer process
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+
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+Starting with a working application from the
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+[Quick Start Guide](quick-start.md), update the `main.js` file
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+with the following lines:
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```javascript
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const { app, BrowserWindow } = require('electron')
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@@ -21,33 +37,39 @@ app.whenReady().then(() => {
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})
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```
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-_online-status.html_
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+create the `online-status.html` file and add the following line before the
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+closing `</body>` tag:
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```html
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-<!DOCTYPE html>
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-<html>
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-<body>
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-<script>
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- const alertOnlineStatus = () => {
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- window.alert(navigator.onLine ? 'online' : 'offline')
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- }
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-
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- window.addEventListener('online', alertOnlineStatus)
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- window.addEventListener('offline', alertOnlineStatus)
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-
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- alertOnlineStatus()
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-</script>
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-</body>
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-</html>
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+<script src="renderer.js"></script>
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+```
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+
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+and add the `renderer.js` file:
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+
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+```javascript
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+const alertOnlineStatus = () => { window.alert(navigator.onLine ? 'online' : 'offline') }
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+
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+window.addEventListener('online', alertOnlineStatus)
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+window.addEventListener('offline', alertOnlineStatus)
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+
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+alertOnlineStatus()
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```
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-There may be instances where you want to respond to these events in the
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-main process as well. The main process however does not have a
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-`navigator` object and thus cannot detect these events directly. Using
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-Electron's inter-process communication utilities, the events can be forwarded
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-to the main process and handled as needed, as shown in the following example.
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+After launching the Electron application, you should see the notification:
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+
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+
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+
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+### Event detection in the Main process
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-_main.js_
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+There may be situations when you want to respond to online/offline events in
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+the Main process as well. The Main process, however, does not have a
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+`navigator` object and cannot detect these events directly. In this case, you
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+need to forward the events to the Main process using Electron's inter-process
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+communication (IPC) utilities.
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+
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+Starting with a working application from the
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+[Quick Start Guide](quick-start.md), update the `main.js` file
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+with the following lines:
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```javascript
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const { app, BrowserWindow, ipcMain } = require('electron')
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@@ -63,23 +85,33 @@ ipcMain.on('online-status-changed', (event, status) => {
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})
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```
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-_online-status.html_
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+create the `online-status.html` file and add the following line before the
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+closing `</body>` tag:
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```html
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-<!DOCTYPE html>
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-<html>
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-<body>
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-<script>
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- const { ipcRenderer } = require('electron')
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- const updateOnlineStatus = () => {
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- ipcRenderer.send('online-status-changed', navigator.onLine ? 'online' : 'offline')
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- }
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-
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- window.addEventListener('online', updateOnlineStatus)
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- window.addEventListener('offline', updateOnlineStatus)
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-
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- updateOnlineStatus()
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-</script>
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-</body>
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-</html>
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+<script src="renderer.js"></script>
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+```
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+
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+and add the `renderer.js` file:
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+
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+```javascript
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+const { ipcRenderer } = require('electron')
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+const updateOnlineStatus = () => { ipcRenderer.send('online-status-changed', navigator.onLine ? 'online' : 'offline') }
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+
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+window.addEventListener('online', updateOnlineStatus)
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+window.addEventListener('offline', updateOnlineStatus)
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+
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+updateOnlineStatus()
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+```
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+
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+After launching the Electron application, you should see the notification in the
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+Console:
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+
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+```sh
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+npm start
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+
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+> [email protected] start /electron
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+> electron .
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+
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+online
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```
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Antonio
