HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

  <meta name=viewport content="width=device-width,initial-scale=1">

  <title>open — JavaScript property</title>

  <style>body{font-family:system-ui,sans-serif;margin:0;padding:1.5rem;background:#f8fafc;color:#334155;line-height:1.7}h1{margin:0 0 .75rem;font-size:1.25rem;color:#0f172a}details{padding:.75rem 1rem;border:1px solid #e2e8f0;border-radius:8px;background:#fff;max-width:420px;margin-bottom:.75rem}summary{cursor:pointer;font-weight:600}#status{padding:.75rem 1rem;border-radius:8px;font-size:.875rem;font-weight:600;max-width:420px;background:#f0fdf4;border:1px solid #bbf7d0;color:#166534}</style>

</head>

<body>

  <h1>details.open = true</h1>

  <p>Script opens the panel on page load.</p>



  <details id=dynamicDetails>

    <summary>Click to toggle</summary>

    <p>This content is opened by JavaScript.</p>

  </details>

  <p id=status aria-live=polite>State: opening…</p>



  <script>var panel=document.getElementById("dynamicDetails"),status=document.getElementById("status");panel.open=!0,status.textContent="State: open (details.open = true)"</script>

</body>

</html>

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HTML open Attribute — dynamic details.open