设置日期的几种格式：
new Date("May 25,2016");
new Date("2016/9/10,12:20:33");
new Date(2016,9,10);
当前系统时间：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>当前系统时间</title>
</head>
<body>
<div>当前时间：<span id="show"></span></div>
<script>
setInterval(function() {
var date = new Date();
var show = document.getElementById('show');
var week = ['星期日','星期一','星期二','星期三','星期四','星期五','星期六'];
//判断数字，数字小于10显示两位数字效果
function checkTime(i) {
if (i < 10) {
i = '0' + i;
}
return i;
}
for (var i = 0; i < week.length; i++) {
if (date.getDay() == i) {
show.innerHTML = week[i] + date.getFullYear() + '年' + checkTime((date.getMonth() + 1)) + '月' + checkTime(date.getDate()) + '日' + checkTime(date.getHours()) + '时' + checkTime(date.getMinutes()) + '分' + checkTime(date.getSeconds()) + '秒' + date.getMilliseconds() + '毫秒';
}
}
}, 1);
</script>
</body>
</html>