popup.js

const groupTabsButton = document.querySelector("#groupTabsButton");

groupTabsButton.addEventListener("click", async () => {
  const tabs = await chrome.tabs.query({ currentWindow: true });

  const ungroupedTabInfo = tabs.map((tab) => {
    const baseUrlMatch = tab.url.match(/https:\/\/([\w\d.]*)\//);

    if (baseUrlMatch === null) {
      return { id: tab.id, baseUrl: null };
    }

    return { id: tab.id, baseUrl: baseUrlMatch[1] };
  });

  const groupedTabIds = ungroupedTabInfo.reduce(
    (acc, cur) => {
      if (cur.baseUrl === null) {
        return { ...acc, 0: [...acc["0"], cur.id] };
      }

      if (Object.keys(acc).includes(cur.baseUrl)) {
        return { ...acc, [cur.baseUrl]: [...acc[cur.baseUrl], cur.id] };
      }

      return { ...acc, [cur.baseUrl]: [cur.id] };
    },
    { 0: [] }
  );

  Object.values(groupedTabIds).forEach((tabIdList) => {
    tabIdList.forEach((tabId) => {
      chrome.tabs.move(tabId, { index: -1 });
    });
  });
});