codice:
<html>
<head><title>hide/show</title>
<script language="javascript" type="text/javascript">
<!--
function hideShow() {
	var a = document.getElementById('a');
	var b = document.getElementById('b');
	if (a.style.display == 'block') {
		a.style.display = 'none';
		b.style.display = 'block';
	} else {
		a.style.display = 'block';
		b.style.display = 'none';
	}
}
//-->
</script>
</head>
<body>
<div id="a" style="display: block;">layer a</div>
<div id="b" style="display: none;">layer b</div>
hideShow
</body>
</html>