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windows.onFocusChanged

files/en-us/mozilla/add-ons/webextensions/api/windows/onfocuschanged/index.md

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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

js-nolint
browser.windows.onFocusChanged.addListener(listener)
browser.windows.onFocusChanged.removeListener(listener)
browser.windows.onFocusChanged.hasListener(listener)

Events have three functions:

  • addListener(listener)
    • : 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

  • listener
    • : The function called when this event occurs. The function is passed this argument:
      • windowId
        • : integer. ID of the newly focused window.

Examples

Log focus changes:

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

{{WebExtExamples}}

Browser compatibility

{{Compat}}

[!NOTE] This API is based on Chromium's chrome.windows API. This documentation is derived from windows.json in the Chromium code.

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