refactor: prefer using app.whenReady() (#21972 )

* docs: add references to app.whenReady() in isReady

* refactor: prefer app.whenReady()

In the docs, specs, and lib, replace instances of `app.once('ready')`
(seen occasionally) and `app.on('ready')` (extremely common) with
`app.whenReady()`.

It's better to encourage users to use whenReady():
1. it handles the edge case of registering for 'ready' after it's fired
2. it avoids the minor wart of leaving an active listener alive for
an event that wll never fire again

2020-02-03 22:43:22 +00:00

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Online/Offline Event Detection

Online and offline event detection can be implemented in the renderer process using the navigator.onLine attribute, part of standard HTML5 API. 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. 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.” Therefore, if you really want to determine the internet access status of Electron, you should develop additional means for checking.

Example:

main.js

const { app, BrowserWindow } = require('electron')

let onlineStatusWindow

app.whenReady().then(() => {
  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 { app, BrowserWindow, ipcMain } = require('electron')
let onlineStatusWindow

app.whenReady().then(() => {
  onlineStatusWindow = new BrowserWindow({ width: 0, height: 0, show: false, webPreferences: { nodeIntegration: true } })
  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>

2.7 KiB Raw Blame History

Online/Offline Event Detection

2.7 KiB

Raw Blame History