index.md

---

title: windows.onFocusChanged
slug: Mozilla/Add-ons/WebExtensions/API/windows/onFocusChanged
page-type: webextension-api-event
tags:
  - API
  - Add-ons
  - Event
  - Extensions
  - Non-standard
  - Reference
  - WebExtensions
  - Windows
  - onFocusChanged
browser-compat: webextensions.api.windows.onFocusChanged

---

{{AddonSidebar()}}

Fired when the currently focused window changes. Will be {{WebExtAPIRef('windows.WINDOW_ID_NONE')}} if all browser windows have lost focus.

Note: In Windows and some Linux window managers, WINDOW_ID_NONE will always be sent immediately preceding a switch from one browser window to another.

Syntax

browser.windows.onFocusChanged.addListener(listener)
browser.windows.onFocusChanged.removeListener(listener)
browser.windows.onFocusChanged.hasListener(listener)

Events have three functions:

• addListener(callback)

  • : Adds a listener to this event.

• removeListener(listener)

  • : Stop listening to this event. The listener argument is the listener to remove.

• hasListener(listener)

  • : Check whether a listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax

Parameters

• callback

  • : Function that will be called when this event occurs. The function will be passed the following arguments:

    • windowId

      • : integer. ID of the newly focused window.

Browser compatibility

{{Compat}}

Examples

Log focus changes:

browser.windows.onFocusChanged.addListener((windowId) => {
  console.log(`Newly focused window: ${windowId}`);
});

{{WebExtExamples}}

Note: This API is based on Chromium's chrome.windows API. This documentation is derived from windows.json in the Chromium code.