HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>required — dynamic toggle</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:360px}label{display:block;margin-bottom:.35rem;font-weight:500;font-size:.875rem}.row{display:flex;align-items:center;gap:.5rem;margin-bottom:.75rem;font-size:.875rem}input[type=email]{width:100%;padding:.5rem .65rem;font:inherit;border:1px solid #cbd5e1;border-radius:6px;box-sizing:border-box;margin-bottom:.75rem}button{padding:.5rem 1.25rem;font:inherit;cursor:pointer;border-radius:6px;border:none;background:#2563eb;color:#fff}#status{margin-top:.75rem;padding:.75rem 1rem;border-radius:8px;font-size:.875rem;background:#f0fdf4;border:1px solid #bbf7d0;color:#166534}</style>

</head>

<body>

  <h1>toggle required</h1>



  <form>

    <label class=row>

      <input type=checkbox id=needEmail checked>

      Require email address

    </label>



    <label for=email>Email:</label>

    <input type=email id=email name=email placeholder=you@example.com>



    <button type=submit>Submit</button>

  </form>



  <p id=status aria-live=polite></p>



  <script>var cb=document.getElementById("needEmail"),email=document.getElementById("email"),status=document.getElementById("status");function sync(){email.required=cb.checked,status.textContent="email.required = "+email.required}cb.addEventListener("change",sync),sync()</script>

</body>

</html>

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HTML required Attribute — dynamic toggle