效果如下：

1.代码如下：

		<h1 id="date_time"></h1>
<script type="text/javascript">
			function Week(option) {
				// switch(option){
				// 	case 0:
				// 	return "星期日";
				// 	case 1:
				// 	return "星期一";
				// 	case 2:
				// 	return "星期二";
				// 	case 3:
				// 	return "星期三";
				// 	case 4:
				// 	return "星期四";
				// 	case 5:
				// 	return "星期五";
				// 	case 6:
				// 	return "星期六";
				// }
				var week = "日一二三四五六".charAt(option);
				return "星期" + week;
			}
            function showTime() {
			var dateTime = new Date();
			var year = dateTime.getFullYear();//年
			var month = dateTime.getMonth() + 1;//月
			month = month < 10 ? "0" + month : month;
			var month1 = month;
			var date = dateTime.getDate();//日
			date = date < 10 ? "0" + date : date;
			var date1 = date;
			var hour = dateTime.getHours();//时
			hour = hour < 10 ? "0" + hour : hour;
			var minute = dateTime.getMinutes();//分
			minute = minute < 10 ? "0" + minute : minute;
			var second = dateTime.getSeconds();//秒
			second = second < 10 ? "0" + second : second;
			var day = dateTime.getDay();
			var week = Week(day);//星期
			dateTime = year + "年" + month1 + "月" + date1 + "日" + " " + week + " " + hour + ":" + minute + ":" + second;
			document.getElementById("date_time").innerHTML = dateTime;
		}
		showTime();
		setInterval("showTime()", 1000);
	</script>