Javascript count list items

<script type="text/javascript">
 
function count(){
var ul = document.getElementById('ulid');
var i=0, c =0;
while(ul.getElementsByTagName('li')[i++]) c++;
alert(c);
}
 
</script>
 
 
<input type="button" onclick="count()";>
<ul id="ulid">
<li>list 1</li>
<li>list 2</li>
<li>list 3</li>
<li>list 4</li>
<li>list 5</li>
</ul>