85 lines
2.7 KiB
Markdown
85 lines
2.7 KiB
Markdown
# 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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Example:
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_main.js_
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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.on('ready', () => {
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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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_online-status.html_
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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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window.addEventListener('online', alertOnlineStatus)
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window.addEventListener('offline', alertOnlineStatus)
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alertOnlineStatus()
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</script>
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</body>
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</html>
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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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_main.js_
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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.on('ready', () => {
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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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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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_online-status.html_
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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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window.addEventListener('online', updateOnlineStatus)
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window.addEventListener('offline', updateOnlineStatus)
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updateOnlineStatus()
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</script>
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</body>
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</html>
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```
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