js获取本日、明天、本周、本月

js获取本日、明天、本周的第一天、本周的最后一天、本月的第一天、本月的最后一天，返回字符串格式的日期：

//本日
function showToDay(){     
    var Nowdate=new Date();     
    M=Number(Nowdate.getMonth())+1     
    return Nowdate.getFullYear()+"-"+M+"-"+Nowdate.getDate();     
}

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

//本周第一天
function showWeekFirstDay(){     
    var Nowdate=new Date();     
    var WeekFirstDay=new Date(Nowdate-(Nowdate.getDay()-1)*86400000);     
    M=Number(WeekFirstDay.getMonth())+1     
    return WeekFirstDay.getFullYear()+"-"+M+"-"+WeekFirstDay.getDate();     
}

//本周最后一天
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.getFullYear()+"-"+M+"-"+WeekLastDay.getDate();     
}

//本月第一天
function showMonthFirstDay(){     
    var Nowdate=new Date();     
    var MonthFirstDay=new Date(Nowdate.getFullYear(),Nowdate.getMonth(),1);     
    M=Number(MonthFirstDay.getMonth())+1;    
    return MonthFirstDay.getFullYear()+"-"+M+"-"+MonthFirstDay.getDate();     
}

//本月最后一天
function showMonthLastDay()     
{     
    var Nowdate=new Date();     
    var MonthNextFirstDay=new Date(Nowdate.getFullYear(),Nowdate.getMonth()+1,1);     
    var MonthLastDay=new Date(MonthNextFirstDay-86400000);     
    M=Number(MonthLastDay.getMonth())+1     
    return MonthLastDay.getFullYear()+"-"+M+"-"+MonthLastDay.getDate();     
}