HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>body replaceChildren</title>
  <style>body{font-family:system-ui,sans-serif;margin:1rem;}</style>
</head>
<body>
  <p id="old">Old content (will be replaced)</p>
  <script>
    var title = document.createElement("h1");
    title.textContent = "Hello again";
    var note = document.createElement("p");
    note.textContent = "Rebuilt with Element.replaceChildren";
    var out = document.createElement("pre");
    document.body.replaceChildren(title, note, out);
    out.textContent = "body children: " + document.body.children.length;
  </script>
</body>
</html>

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body.replaceChildren — everyday UI rebuild (Try It)