<script>
function $(id){
    return document.getElementById(id);
}
</script>
<div style="display:none" id="myblock">
    <input>
    <input>
    <input>
</div>
<button id="button">Добавить</button>
<script>
(function(){
    var block = $('myblock').parentNode.removeChild($('myblock'));
    block.style.display = 'block';
    $('button').addEventListener('click', function(){
        document.body.appendChild(block.cloneNode(true));
    });
})();
</script>