contentScript.js

let updateStatus = true;
let lastSavedStatus;

chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
  if (request.operation === "checkStatus") {
    // We wait 500 ms so that the XUI scripts
    // have time to inject the result into the DOM
    setTimeout(checkIfStandby, 500);
  } else if (request.operation === "stopUpdating") {
    updateStatus = false;
    document.body.classList.remove("standby-lb-detector-css");
  }
});

const checkIfStandby = () => {
  const statusInfo = document.getElementById("status").innerText.toLowerCase();

  if (status !== lastSavedStatus) {
    if (statusInfo.includes("standby")) {
      saveStatus("standby");
      if (updateStatus) {
        document.body.className = "standby-lb-detector-css";
        chrome.runtime.sendMessage({ operation: "activateButton" });
      }
    } else {
      // We enable updating if the box is active
      // So that we notify if the box goes standby -> active -> standby
      saveStatus("active");
      updateStatus = true;
      document.body.classList.remove("standby-lb-detector-css");
      chrome.runtime.sendMessage({ operation: "deactivateButton" });
    }
  }
};

const saveStatus = status => {
  chrome.storage.local.set(
    {
      [location.hostname]: status
    },
    () => {
      lastSavedStatus = status;
    }
  );
};