var img = document.getElementById("img");
var number = 1;
function fun() {
number++;
if (number>3){
number=1;
}
img.src="img/banner_"+number+".jpg";
}
setInterval(fun,3000);
var off = document.getElementById("off");
function fun2() {
off.src="img/on.gif";
}
setTimeout(fun2,5000);
</script>
</body>
</html>