<html>
<body>
<script language="JavaScript">
function newElem(myT) {
var newI = document.createElement("LI")
newI.innerHTML = myT
return newI}
function function1(form) {
var newI = newElem(form.enter.value);
var fLi = document.getElementById("myList").firstChild;
document.getElementById("myList").replaceChild(newI, fLi);}
function function2(form) {
var newI = newElem(form.enter.value);
var fLi = document.getElementById("myList").lastChild;
document.getElementById("myList").replaceChild(newI, fLi);}
</script>
<form>
<input type="text" name="enter" size="50">
<button onClick="function1(this.form);"> Replace first item</button>
<button onClick="function2(this.form);"> Replace last item</button>
<ul id="myList">
<li>First List Item</li>
<li>Second List Item</li>
</ul>
</form>
</body>
</html>