html5 input type required without a form. Does it work?
<input type='text' required>

<input id='name' type='text' required>
    <input id='surname' type='text' required>
    <input id='send' type='button' onclick ='send()'>

    function send() {
       if (document.getElementById('name').value == '') { alert('missing name'); return }
       if (document.getElementById('surname').value == '') { alert('missing surname'); return }

       // logic now...

    }