输出有问题
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>获得星期</title>
<script type="text/javascript">
var mydate=new Date(2019,8,18);
document.write(mydate+"<br/>")
var weekday=["星期日","星期一","星期二","星期三","星期四","星期五","星期六"];
document.write("今天是：" +weekday[mydate.getDay()]);
</script>
</head>
<body>
</body>
</html>
结果应该是星期天 实际输出星期三
