The second result is more semantically correct, but it will not function if called on tr.athing because tr.athing contains HTML elements that will be deleted when you replace the text. It is still much safer than innerHTML which will silently corrupt attributes. It's also interesting you need to prompt Codex for security best practices (and a bit questionable if it even "knows" anything about best practices)

I guess part of it is that a one-liner is impossible. Here's what I would write given the prompt

    const makeUppercase = (id) => {
      const element = document.getElementById(id);
      if (element == null) return;
      const makeChildNodeUpper = (node) => {
        if (node.nodeType === Node.TEXT_NODE) {
          node.nodeValue = node.nodeValue.toUpperCase();
        } else {
          node.childNodes.forEach(makeChildNodeUpper);
        }
      }
      makeChildNodeUpper(element);
    }