HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>toggleAttribute guard</title>
  <style>body{font-family:sans-serif;margin:1rem;} pre{background:#f3f4f6;padding:0.75rem;border-radius:6px;}</style>
</head>
<body>
  <button type="button" id="run">Run demo</button>
  <pre id="out">Click Run</pre>
  <script>
    document.getElementById("run").addEventListener("click", function () {
      var el = document.createElement("div");
      var lines = [];
      try {
        el.toggleAttribute("ok-name");
        lines.push("ok-name toggled");
        el.toggleAttribute("bad name");
      } catch (err) {
        lines.push(err.name);
      }
      document.getElementById("out").textContent = lines.join("\n");
    });
  </script>
</body>
</html>

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Element.toggleAttribute — invalid name (Try It)