js 计算月/周的第一天和最后一天代码

//获取当前日期yy-mm-dd
//date 为时间对象
function getDateStr3(date) {
  var year = "";
  var month = "";
  var day = "";
  var now = date;
  year = ""+now.getFullYear();
  if((now.getMonth()+1)<10){
    month = "0"+(now.getMonth()+1);
  }else{
    month = ""+(now.getMonth()+1);
  }
  if((now.getDate())<10){
    day = "0"+(now.getDate());
  }else{
    day = ""+(now.getDate());
  }
  return year+"-"+month+"-"+day;
}
/ 
 获得相对当前周AddWeekCount个周的起止日期 
 AddWeekCount为0代表当前周  为-1代表上一个周  为1代表下一个周以此类推
 / 
function getWeekStartAndEnd(AddWeekCount) { 
  //起止日期数组  
  var startS = new Array(); 
  //一天的毫秒数  
  var millisecond = 1000  60  60  24; 
  //获取当前时间  
  var currentDate = new Date();
  //相对于当前日期AddWeekCount个周的日期
  currentDate = new Date(currentDate.getTime() + (millisecond  7AddWeekCount));
  //返回date是一周中的某一天
  var week = currentDate.getDay(); 
  //返回date是一个月中的某一天  
  var month = currentDate.getDate();
  //减去的天数  
  var minusDay = week != 0 ? week - 1 : 6; 
  //获得当前周的第一天  
  var currentWeekFirstDay = new Date(currentDate.getTime() - (millisecond  minusDay)); 
  //获得当前周的一天
   var currentWeekLastDay = new Date(currentWeekFirstDay.getTime() + (millisecond  6));
  //添加至数组  
  startS.push(getDateStr3(currentWeekFirstDay)); 
  startS.push(getDateStr3(currentWeekLastDay)); 
  
  return startS; 
} 
/ 
 获得相对当月AddMonthCount个月的起止日期 
 AddMonthCount为0 代表当月 为-1代表上一个月 为1代表下一个月 以此类推
 / 
function getMonthStartAndEnd(AddMonthCount) { 
  //起止日期数组  
  var startS = new Array(); 
  //获取当前时间  
  var currentDate = new Date();
  var month=currentDate.getMonth()+AddMonthCount;
  if(month<0){
    var n = parseInt((-month)/12);
    month += n12;
    currentDate.setFullYear(currentDate.getFullYear()-n);
  }
  currentDate = new Date(currentDate.setMonth(month));
  //获得当前月份0-11  
  var currentMonth = currentDate.getMonth(); 
  //获得当前年份4位年  
  var currentYear = currentDate.getFullYear(); 
  //获得上一个月的第一天  
  var currentMonthFirstDay = new Date(currentYear, currentMonth,1); 
  //获得上一月的一天  
  var currentMonthLastDay = new Date(currentYear, currentMonth+1, 0); 
  //添加至数组  
  startS.push(getDateStr3(currentMonthFirstDay)); 
  startS.push(getDateStr3(currentMonthLastDay)); 
  //返回  
  return startS; 
}

//获取到每月的第一天和一天
 getMonthFirstOrLaseDay:function(month){
        var month=month || (new Date()).getMonth() //设置默认 如果不穿 取当前月份
    var nowdays = new Date(); 
    var year = nowdays.getFullYear(); 
    if(month==0) { 
      month=12; 
      year=year-1; 
    } 
    if (month < 10) { 
      month = "0" + month; 
    } 
    var firstDay = year+'' + month+'' + "01";
    var myDate = new Date(year, month, 0); 
    var lastDay = year+'' + month+'' + myDate.getDate();
    return {firstDay:firstDay,lastDay:lastDay}
  },

//获取到每个月有几周，并且每周一和周日是哪天
 getAForWeeks:function (year, month) {
  var year=year || (new Date()).getFullYear()
  var month=month || (new Date()).getMonth()


  var d = new Date();
  // what day is first day
  d.setFullYear(year, month-1, 1);
  var w1 = d.getDay();
  if (w1 == 0) w1 = 7;
  // total day of month
  d.setFullYear(year, month, 0);
  var dd = d.getDate();
  // first Monday
  if (w1 != 1) d1 = 7 - w1 + 2;
  else d1 = 1;
  week_count = Math.ceil((dd-d1+1)/7);
  var allWeek={};
  for (var i = 0; i < week_count; i++) {
    var monday = d1+i7;
    var sunday = monday + 6;
    var from = year+''+this.fnToDub(month)+''+this.fnToDub(monday);
    var to;
    if (sunday <= dd) {
      to = year+''+this.fnToDub(month)+''+this.fnToDub(sunday);
    } else {
      d.setFullYear(year, month-1, sunday);
      to = d.getFullYear()+''+this.fnToDub((d.getMonth()+1))+''+this.fnToDub(d.getDate());
    }
    allWeek[(i+1)]={
     from:from,
     to:to
    }
  }
  return {allWeek:allWeek,week_count:week_count}
 },

var date = new Date(), y = date.getFullYear(), m = date.getMonth();
var firstDay = new Date(y, m, 1);
var lastDay = new Date(y, m + 1, 0);

var date = new Date();
var firstDay = new Date(date.getFullYear(), date.getMonth(), 1);
var lastDay = new Date(date.getFullYear(), date.getMonth() + 1, 0);

var y = 2012, m = 1
var firstDay = new Date(y, m - 1, 1);
var lastDay = new Date(y, m, 0);
console.log(firstDay);
console.log(lastDay);