function replaceMessage(){
var new1=document.createElement("i");
var new11=document.createTextNode("JavaScript");
new1.appendChild(new11);
var oldNode=document.getElementById("oldnode");
oldNode.parentNode.replaceChild(new1,oldnode);
}
<script type="text/javascript">
function replaceMessage(){
var newnode=document.createElement("i");
var newnodeText=document.createTextNode("JavaScript");
newnode.appendChild(newnodeText);
var oldnode=document.getElementById("oldnode");
oldnode.parentNode.replaceChild(newnode,oldnode);
}
</script>