Edit in JSFiddle

<body>
<div id="dfn">
</div>
<input type="button" id="b1" value="Press" onclick="dfn()">
</body>

function dfn()
{
var element=document.createElement("dfn");
var text=document.createTextNode("This is dfn effect.");
element.appendChild(text);
document.getElementById("dfn").appendChild(element);
}