<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
</body>
</html>
<script type="text/javascript">
var runNian = parseInt(prompt("请输入年份"))
if(runNian%4 == 0 && runNian%100 !== 0 || runNian%400 ==0 ) {
alert("闰年")
}
else{
alert("不是闰年")
}
</script>
原文：https://www.cnblogs.com/hankai2735/p/8760947.html