TubeFocus

// One writer keeps edits from separate popup/options pages from overwriting one another.
chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
  if (message?.type !== 'tubefocus:settings' || sender?.id !== chrome.runtime.id) return;
  // Only extension pages may use this message API for settings writes.
  if (![chrome.runtime.getURL('popup.html'), chrome.runtime.getURL('settings.html')].includes(sender.url)) {
    sendResponse({ ok: false, error: 'Open TubeFocus to change settings.' });
    return false;
  }
  let command;
  try { command = parseCommand(message); } catch (error) {
    sendResponse({ ok: false, error: error.message });
    return false;
  }
  if (pendingWrites >= MAX_PENDING_WRITES) {
    sendResponse({ ok: false, error: 'Too many changes. Please wait a moment and try again.' });
    return false;
  }
  pendingWrites++;
  const operation = writeQueue.then(async () => {
    const current = await readSettings();
    // … the command, applied to the settings it just read, and saved …
  });
  writeQueue = operation.catch(() => {});