HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>item bracket</title>
</head>
<body>
  <div id="demo" class="card" data-role="panel">Demo</div>
  <pre id="out">Waiting...</pre>
  <script>
    var map = document.querySelector("#demo").attributes;
    var byIndex = map.item(0);
    var byBracketIndex = map[0];
    var byName = map["id"];
    document.getElementById("out").textContent = String(byIndex === byBracketIndex) + " " + byName.name + " " + byName.value;
  </script>
</body>
</html>

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NamedNodeMap.item() — numeric vs string bracket (Try It)