old_contents: let backtrace = document.querySelector(".Flow-Debug-Exception-Backtrace-Code");
  let localStorageItemIdentifier = 'Flow-Debug-Exception-Backtrace-Code-Open';
  
  if (window.localStorage.getItem(localStorageItemIdentifier) === "true") {
      backtrace.open = true;
  }
  
  backtrace.addEventListener("click", (event) => {
      if (backtrace.open === true) {
          window.localStorage.removeItem(localStorageItemIdentifier);
      } else {
          window.localStorage.setItem(localStorageItemIdentifier, true);
      }
  });
new_contents: const backtrace = document.querySelector(".Flow-Debug-Exception-Backtrace-Code");
  const localStorageItemIdentifier = 'Flow-Debug-Exception-Backtrace-Code-Open';
  
  if (window.localStorage.getItem(localStorageItemIdentifier) === "true") {
      backtrace.open = true;
  }
  
  backtrace.addEventListener("click", (event) => {
      if (backtrace.open === true) {
          window.localStorage.removeItem(localStorageItemIdentifier);
      } else {
          window.localStorage.setItem(localStorageItemIdentifier, true);
      }
  });
  
subject: Change JS variables to constants