5c6fa7e420
* docs: revised the online-offline event detection feature page * docs: fixed text and grammar mentions
117 lines
3.5 KiB
Markdown
117 lines
3.5 KiB
Markdown
# Online/Offline Event Detection
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## Overview
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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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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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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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## Example
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### Event detection in the Renderer process
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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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let onlineStatusWindow
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app.whenReady().then(() => {
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onlineStatusWindow = new BrowserWindow({ width: 0, height: 0, show: false })
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onlineStatusWindow.loadURL(`file://${__dirname}/online-status.html`)
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})
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```
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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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<script src="renderer.js"></script>
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```
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and add the `renderer.js` file:
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```javascript
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const alertOnlineStatus = () => { window.alert(navigator.onLine ? 'online' : 'offline') }
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window.addEventListener('online', alertOnlineStatus)
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window.addEventListener('offline', alertOnlineStatus)
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alertOnlineStatus()
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```
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After launching the Electron application, you should see the notification:
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### Event detection in the Main process
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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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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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let onlineStatusWindow
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app.whenReady().then(() => {
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onlineStatusWindow = new BrowserWindow({ width: 0, height: 0, show: false, webPreferences: { nodeIntegration: true } })
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onlineStatusWindow.loadURL(`file://${__dirname}/online-status.html`)
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})
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ipcMain.on('online-status-changed', (event, status) => {
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console.log(status)
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})
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```
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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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<script src="renderer.js"></script>
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```
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and add the `renderer.js` file:
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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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window.addEventListener('online', updateOnlineStatus)
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window.addEventListener('offline', updateOnlineStatus)
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updateOnlineStatus()
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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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```sh
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npm start
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> electron@1.0.0 start /electron
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> electron .
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online
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```
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