mirror of https://github.com/electron/electron
90 lines
2.8 KiB
Markdown
90 lines
2.8 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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Starting with an HTML file `index.html`, this example will demonstrate how the `navigator.onLine` API can be used to build a connection status indicator.
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```html title="index.html"
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="UTF-8">
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<title>Hello World!</title>
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<meta http-equiv="Content-Security-Policy" content="script-src 'self' 'unsafe-inline';" />
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</head>
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<body>
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<h1>Connection status: <strong id='status'></strong></h1>
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<script src="renderer.js"></script>
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</body>
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</html>
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```
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In order to mutate the DOM, create a `renderer.js` file that adds event listeners to the `'online'` and `'offline'` `window` events. The event handler sets the content of the `<strong id='status'>` element depending on the result of `navigator.onLine`.
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```js title='renderer.js'
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const updateOnlineStatus = () => {
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document.getElementById('status').innerHTML = 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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```
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Finally, create a `main.js` file for main process that creates the window.
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```js title='main.js'
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const { app, BrowserWindow } = require('electron')
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const createWindow = () => {
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const onlineStatusWindow = new BrowserWindow({
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width: 400,
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height: 100
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})
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onlineStatusWindow.loadFile('index.html')
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}
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app.whenReady().then(() => {
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createWindow()
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app.on('activate', () => {
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if (BrowserWindow.getAllWindows().length === 0) {
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createWindow()
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}
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})
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})
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app.on('window-all-closed', () => {
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if (process.platform !== 'darwin') {
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app.quit()
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}
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})
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```
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After launching the Electron application, you should see the notification:
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> Note: If you need to communicate the connection status to the main process, use the [IPC renderer](../api/ipc-renderer.md) API.
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