storage.onChanged

browser.storage.onChanged.addListener(listener)
browser.storage.onChanged.removeListener(listener)
browser.storage.onChanged.hasListener(listener)

/*
Log the storage area that changed,
then for each item changed,
log its old value and its new value.
*/
function logStorageChange(changes, area) {
  console.log(`Change in storage area: ${area}`);
  const changedItems = Object.keys(changes);
  for (const item of changedItems) {
    console.log(`${item} has changed:`);
    console.log("Old value: ", changes[item].oldValue);
    console.log("New value: ", changes[item].newValue);
  }
}
browser.storage.onChanged.addListener(logStorageChange);