javascript算出上週的時間區間

<script type="text/javascript">
			var datestr = "";
			var beforeDate = new Date();
			beforeDate.setTime(beforeDate.getTime()-1000*60*60*24*7-((beforeDate.getDay()==0?7:beforeDate.getDay())-1)*24*60*60*1000);
			var strYear=beforeDate.getFullYear();
			var strMon=beforeDate.getMonth()+1;
			var strDate=beforeDate.getDate();

			datestr = "統計區間："+strYear+"-"+strMon+"-"+strDate+"至";

			beforeDate.setTime(beforeDate.getTime()+(7-beforeDate.getDay())*24*60*60*1000);

			strYear=beforeDate.getFullYear();

			strMon=beforeDate.getMonth()+1;

			strDate=beforeDate.getDate();

			datestr += strYear+"-"+strMon+"-"+strDate;

			alert(datestr);

			</script>