HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>shadowRoot open</title>
</head>
<body>
  <div id="host"></div>
  <pre id="out"></pre>
  <script>
    var host = document.getElementById("host");
    host.attachShadow({ mode: "open" });
    var lines = [];
    lines.push("has shadowRoot: " + !!host.shadowRoot);
    lines.push("mode: " + host.shadowRoot.mode);
    document.getElementById("out").textContent = lines.join("\n");
  </script>
</body>
</html>

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Element.shadowRoot — open mode (Try It)