<html>
<script type="text/javascript">
<!--
function toggle_visibility(id) {
var e = document.getElementById(id);
if(e.style.display == 'block')
e.style.display = 'none';
else
e.style.display = 'block';
}
//-->
</script>
<body>
<a href="#" onclick="toggle_visibility('foo');">Click here</a>
<div id="foo">This is foo</div>
</body>
</html>