计时器完成轮播图效果
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>轮播图</title>
</head>
<body>
<img src="banner_1.jpg" width="100%" id="img">
<script>
var num = 1;
function f() {
num = num + 1;
if (num > 3) {
num = 1;
}
var elementById = document.getElementById("img");
elementById.src = "banner_" + num + ".jpg";
}
setInterval("f()", 3000);
</script>
</body>
</html>
