用javascript 取到当前月第一天、最后一天，本周第一天、最后一天

<script language=javascript>
function showWeekFirstDay()
{
var Nowdate=new Date();
var WeekFirstDay=new Date(Nowdate-(Nowdate.getDay()-1)*86400000);
alert(WeekFirstDay)
}
function showWeekLastDay()
{
var Nowdate=new Date();
var WeekFirstDay=new Date(Nowdate-(Nowdate.getDay()-1)*86400000);
var WeekLastDay=new Date((WeekFirstDay/1000+6*86400)*1000);
alert(WeekLastDay)
}
function showMonthFirstDay()
{
var Nowdate=new Date();
var MonthFirstDay=new Date(Nowdate.getYear(),Nowdate.getMonth(),1);
alert(MonthFirstDay)
}
function showMonthLastDay()
{
var Nowdate=new Date();
var MonthNextFirstDay=new Date(Nowdate.getYear(),Nowdate.getMonth()+1,1);
var MonthLastDay=new Date(MonthNextFirstDay-86400000);
alert(MonthLastDay)
}
</script>