I could imagine a page where cutting HTML would cause it be a yes (not exact JS).

  <script>
    setTimeout(10000, () => {
      safeEval(<some user input>);
    });
  </script>
  <script>
    window.safeEval = code => eval(code);
  </script>

  <!-- cut the page here -->
  <!-- the prev and next tags around this comment could be combined in one and cut in the middle if the browser autocloses them and treats as valid script after -->

  <script>
    <!-- safety fixed! -->
    const notTooSafe = window.safeEval;
    
    window.safeEval = code => {
      if (code.any(c => !c.isDigit())) throw "unsafe";
      return notTooSafe(code);
    };
  </script>