<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title></title>
<style type="text/css">
.bloque {
display: block;
width: 100px;
height: 100px;
background-color: grey;
}
</style>
<script type="text/javascript">
var arrcolor = ['green', 'yellow', 'red'];
var counter = 0;
function semaforo() {
document.getElementById('b'+counter % arrcolor.length).style.backgroundColor = arrcolor[counter % arrcolor.length];
if (counter % arrcolor.length != 0 || (counter-1) % arrcolor.length == 2) {
document.getElementById('b'+(counter-1) % arrcolor.length).style.backgroundColor = 'grey';
}
counter++;
}
</script>
</head>
<body>
<div class="bloque" id="b0"></div>
<div class="bloque" id="b1"></div>
<div class="bloque" id="b2"></div>
<button onclick="semaforo()">cambiar semaforo</button>
</body>
</html>