I recently updated to latest macOS and one page of my flask app stopped working when running on localhost.

I am extending simple layout.html with another html page. At the end of this extend page I have following script:

<script type="text/javascript">
  var oReq = new XMLHttpRequest();
  oReq.addEventListener("load", (function(xhr) {
                var code = xhr.currentTarget.response;
                var codeBlock = document.getElementById("code");
                codeBlock.textContent = code;
                hljs.highlightBlock(codeBlock);
            }));
    oReq.open("GET", "{{ url_for('static', filename='extend.js') }}");       

  </script>

I get error:

Uncaught TypeError: codeBlock is null

Everything worked fine until I updated to Monterey. Any help in resolving this is appreciated.