根据insertBefore()衍生出来的insertAfter()函数

function insertAfter(newElement.targetElement){

var parent=targetElement.parentNode;

if(parent.lastChild == targetElement){

parent.appendChild(newElement);

}else{

parent.insertBefore(newElement,targetElement.nextSibling);

}

}

<script type="text/javascript">

var oTest = document.getElementById("test");

var newNode = document.createElement("h2");

newNode.innerHTML = "This is a test";

oTest.insertBefore(newNode,null);

var newNode1 = document.createElement("h3");

newNode1.innerHTML = "This is a test 333";

oTest.insertBefore(newNode1,newNode);

</script>

<script type="text/javascript">

var oTest = document.getElementById("test");

var x1= document.getElementById("x1");

var x2= document.getElementById("x2");

var newNode = document.createElement("h2");

newNode.innerHTML = "This is a test";

oTest.insertBefore(newNode,x2.previousSibling);

</script>

<script type="text/javascript">

var oTest = document.getElementById("test");

var x2= document.getElementById("x2");

var newNode = document.createElement("h2");

newNode.innerHTML = "This is a test";

oTest.insertBefore(newNode,x2);

</script>

<script type="text/javascript">

var oTest = document.getElementById("test");

var newNode = document.createElement("h2");

newNode.innerHTML = "This is a test";

oTest.insertBefore(newNode,oTest.childNodes[1]);

</script>