<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<script type="text/javascript">
//for(var i = 5; i > 0; i++) { 没有结束条件会陷入无限循环，把网页卡死
for(var i = 5; i > 0; i--) {
document.write(i,",");
}
</script>
</head>
<body>
</body>
</html>
返回值：
5,4,3,2,1,