JS格式化日期

<form name="form1" method="post" action="">
		请输入所要查询的时间范围<br>
	起始日期：<input type="text" id="begainDate" name="begainDate" readonly onclick="WdatePicker({firstDayOfWeek:7})"  style="width: 70px" > ~ 
	结束日期：<input type="text" id="endDate" name="endDate" readonly onclick="WdatePicker({firstDayOfWeek:7})"  style="width: 70px" >
	<input type="button" value="确认" onblur="checkTime()">
 <script language="javascript">
  Date.prototype.format = function(format)
        {
                var o =
                {
                    "M+" : this.getMonth()+1, //month
                    "d+" : this.getDate(),    //day
                    "h+" : this.getHours(),   //hour
                    "m+" : this.getMinutes(), //minute
                    "s+" : this.getSeconds(), //second
                    "q+" : Math.floor((this.getMonth()+3)/3), //quarter
                    "S" : this.getMilliseconds() //millisecond
                }
               
                if(/(y+)/.test(format))
                format=format.replace(RegExp.$1,(this.getFullYear()+"").substr(4 - RegExp.$1.length));
                for(var k in o)
                if(new RegExp("("+ k +")").test(format))
                format = format.replace(RegExp.$1,RegExp.$1.length==1 ? o[k] : ("00"+ o[k]).substr((""+ o[k]).length));
                return format;
        }
       
      


var now = new Date();

now.setMonth(now.getMonth()-3);
now.setDate(now.getDate()-1); 

var endNow = new Date();
endNow.setMonth(endNow.getMonth()-3);

var startDate=now.format('yyyy-MM-dd');
var endDate = endNow.format('yyyy-MM-dd');
document.getElementById("begainDate").value=startDate;
document.getElementById("endDate").value=endDate;
</script>	
	
	
	
</form>

PS：留作纪念。。时间久了会忘的。