sessions.onChanged - Mozilla

Syntax

browser.sessions.onChanged.addListener(listener)
browser.sessions.onChanged.removeListener(listener)
browser.sessions.onChanged.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 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. It's passed no parameters.

Examples

This very annoying extension listens for onChanged, then immediately restores the most recently closed session, thus making it impossible to close windows or tabs:

function restoreSession(sessionInfos) {
  if (!sessionInfos.length) {
    console.log("No sessions found");
    return;
  }
  let sessionInfo = sessionInfos[0];
  if (sessionInfo.tab) {
    browser.sessions.restore(sessionInfo.tab.sessionId);
  } else {
    browser.sessions.restore(sessionInfo.window.sessionId);
  }
}

function onError(error) {
  console.log(error);
}

function restoreMostRecent() {
  let gettingSessions = browser.sessions.getRecentlyClosed({
    maxResults: 1,
  });
  gettingSessions.then(restoreSession, onError);
}

browser.sessions.onChanged.addListener(restoreMostRecent);

Browser compatibility

Note: This API is based on Chromium's chrome.sessions API.

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This page was last modified on ⁨Jul 17, 2025⁩ by MDN contributors.

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