On Windows a taskbar button can be used to display a progress bar. This enables a window to provide progress information to the user without the user having to switch to the window itself.
On macOS the progress bar will be displayed as a part of the dock icon.
The Unity DE also has a similar feature that allows you to specify the progress bar in the launcher.
Progress bar in taskbar button:

All three cases are covered by the same API - the setProgressBar() method
  available on instances of BrowserWindows. Call it with a number between 0
  and 1 to indicate your progress. If you have a long-running task that's
  currently at 63% towards completion, you'd call it with setProgressBar(0.63).
Generally speaking, setting the parameter to a value below zero (like -1)
  will remove the progress bar while setting it to a value higher than one
  (like 2) will switch the progress bar to intermediate mode.
See the API documentation for more options and modes.
const { BrowserWindow } = require('electron')
  const win = new BrowserWindow()
  
  win.setProgressBar(0.5)