test.js

 let mutationObserver;

 TXTextControl.addEventListener("textControlLoaded", function () {
     TXTextControl.addEventListener("webSocketClosed", (e) => {
         observeDisconnect("#txErrMsgDiv");
     });
 });

 function observeDisconnect(selector) {
     const el = document.querySelector(selector);

     mutationObserver = new MutationObserver((mutationRecords, observer) => {
         Array.from(document.querySelectorAll(selector)).forEach((element) => {
             if (element.innerText.includes("Reconnecting")) {
                 element.innerHTML =
                     "<strong>Please wait!</strong> We are working on it!<br /><br /><div style='vertical-align: middle;' class='spinner-border' role='status'><span class='sr-only'></span></div>";
             }

             observer.disconnect();
         });
     }).observe(document.documentElement, {
         childList: true,
         subtree: true,
         characterData: false,
     });
 }