js如何获取本日本周本月的时间代码

function showToDay() 
{ 
 var Nowdate=new Date(); 
 M=Number(Nowdate.getMonth())+1 
 alert(Nowdate.getMonth()+"月,"+Nowdate.getDate()+"号,星期"+Nowdate.getDay()); 
 return Nowdate.getYear()+"-"+M+"-"+Nowdate.getDate(); 
}

function showTomorrow()
{ 
 var tom=new Date(); 
 tom.setDate(tom.getDate()+1); 
 M=Number(tom.getMonth())+1 
 return tom.getYear()+"-"+M+"-"+tom.getDate(); 
}

function showWeekFirstDay() 
{ 
 var Nowdate=new Date(); 
 var WeekFirstDay=new Date(Nowdate-(Nowdate.getDay()-1)*86400000); 
 M=Number(WeekFirstDay.getMonth())+1 
 return WeekFirstDay.getYear()+"-"+M+"-"+WeekFirstDay.getDate(); 
}

function showWeekLastDay() 
{ 
 var Nowdate=new Date(); 
 var WeekFirstDay=new Date(Nowdate-(Nowdate.getDay()-1)*86400000); 
 var WeekLastDay=new Date((WeekFirstDay/1000+6*86400)*1000); 
 M=Number(WeekLastDay.getMonth())+1 
 return WeekLastDay.getYear()+"-"+M+"-"+WeekLastDay.getDate(); 
}

function showMonthFirstDay() 
{ 
 var Nowdate=new Date(); 
 var MonthFirstDay=new Date(Nowdate.getYear(),Nowdate.getMonth(),1); 
 M=Number(MonthFirstDay.getMonth())+1 
 return MonthFirstDay.getYear()+"-"+M+"-"+MonthFirstDay.getDate(); 
}

function showMonthLastDay() 
{ 
 var Nowdate=new Date(); 
 var MonthNextFirstDay=new Date(Nowdate.getYear(),Nowdate.getMonth()+1,1); 
 var MonthLastDay=new Date(MonthNextFirstDay-86400000); 
 M=Number(MonthLastDay.getMonth())+1 
 return MonthLastDay.getYear()+"-"+M+"-"+MonthLastDay.getDate(); 
}

function getTime(s)
{ 
 var time1=document.getElementById("num1"); 
 var time2=document.getElementById("num2"); 
 if(s==1){ 
 //本日时间 
 time1.value=showToDay(); 
 //alert("今日:"+time1.value); 
 time2.value=showTomorrow(); 
 //alert("今日:"+time2.value); 
 }else if(s==2){ 
 //本周时间 
 time1.value=showWeekFirstDay(); 
 //alert("本月第一天:"+time1.value); 
 time2.value=showWeekLastDay(); 
 //alert("本月最后一天:"+time2.value); 
 }else{ 
 //本月时间 
 time1.value=showMonthFirstDay(); 
 //alert("本月第一天"+time1.value); 
 time2.value=showMonthLastDay(); 
 //alert("本月最后一天"+time2.value); }
}