HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onsubmit — dynamic handler</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}form{max-width:420px;padding:1rem;background:#fff;border:1px solid #e2e8f0;border-radius:8px}label{display:block;margin-bottom:.25rem;font-weight:600;font-size:.875rem}input[type=text]{width:100%;padding:.5rem .75rem;margin-bottom:.75rem;border:1px solid #cbd5e1;border-radius:6px;box-sizing:border-box}input[type=submit]{padding:.5rem 1rem;border:none;border-radius:6px;background:#2563eb;color:#fff;font-weight:600;cursor:pointer}#log{margin-top:.75rem;padding:.75rem 1rem;border-radius:8px;font-size:.875rem;max-width:420px;background:#f1f5f9;border:1px solid #e2e8f0;color:#475569}</style>

</head>

<body>

  <h1>dynamicForm.onsubmit</h1>

  <p>Handler attached in script — submit to see the log update.</p>



  <form id=dynamicForm action=#>

    <label for=name>Name</label>

    <input id=name name=name required>

    <input type=submit value=Submit>

  </form>

  <div id=log aria-live=polite>Waiting for submit…</div>



  <script>document.getElementById("dynamicForm").onsubmit=function(){var e=document.getElementById("log");return e.textContent="Form submitted dynamically — handler ran before navigation.",e.style.background="#f0fdf4",e.style.borderColor="#bbf7d0",e.style.color="#166534",!1}</script>

</body>

</html>

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HTML onsubmit Attribute — dynamic handler