HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>Toggle disabled</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:.35rem;font-size:.875rem;font-weight:600;color:#475569}input{width:100%;box-sizing:border-box;font:inherit;padding:.45rem .6rem;border:1px solid #cbd5e1;border-radius:6px}button{margin-top:.85rem;font:inherit;padding:.45rem .85rem;border:1px solid #2563eb;border-radius:6px;background:#2563eb;color:#fff;cursor:pointer}button:disabled{background:#94a3b8;border-color:#94a3b8;cursor:not-allowed}p{font-size:.875rem;color:#64748b;max-width:420px;margin-top:1rem}code{background:#e2e8f0;padding:.1rem .35rem;border-radius:4px}</style>

</head>

<body>

  <h1>Enable button when input is valid</h1>

  <form action=# onsubmit=return!1>

    <label for=name>Name</label>

    <input id=name name=name placeholder="Enter your name">



    <button type=submit id=submitBtn disabled>Submit</button>

  </form>

  <p>Type a name to remove <code>disabled</code>. Use <code>element.disabled = true/false</code> or <code>setAttribute</code> / <code>removeAttribute</code>.</p>

  <script>var nameInput=document.getElementById("name"),submitButton=document.getElementById("submitBtn");nameInput.addEventListener("input",(function(){submitButton.disabled=""===nameInput.value.trim()}))</script>

</body>

</html>

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HTML disabled Attribute — Toggle with JavaScript