<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
</head>
<body>
<script type="text/javascript">
var randomNumber = Math.floor(Math.random() * 1000) + 1000; // 生成 4 位随机数字
alert(randomNumber);
</script>
</body>
</html>