<div id="test">
</div>
<script>
var a = document.createElement('p');
a.innerHTML = '안녕';
document.querySelector('#test').appendChild(a);
</script>
<div id="test">
</div>
<script>
var a = '<p>안녕</p>';
document.querySelector('#test').insertAdjacentHTML('beforeend', a);
</script>