JS获取今天是本月第几周、本月共几周、本月有多

// 获取某年某月的有多少周
String.prototype.weekInMonthCount = function () {
  var date = new Date((new Date(this).setDate(1)) || (new Date()).setDate(1));
  var firstWeekDate = 1;// 默认第一周是本月1号 为了模拟本月1号是否为本月第1周的判断
  if (date.getDay() === 1) { // 判断1号是周一
    firstWeekDatek = 1;
  } else if (date.getDay() === 0) { // 判断1号是周日
    firstWeekDate = 8 - 7 + 1;
  } else { // 判断1号是周二至周六之间
    firstWeekDate = 8 - date.getDay() + 1;
  }
  date.setMonth(date.getMonth()+1);
  date.setDate(0);
  var monthHasDays = date.getDate();// 本月天数
  monthHasDays = date.getDate() - firstWeekDate + 1;
  var hasWeek = Math.ceil(monthHasDays/7); // 计算本月有几周
  return hasWeek;
};
// 获取今天是今年的第几周
String.prototype.weekIndexInYear = function () {
  var nowDate = new Date(this != '' ? this : new Date());
  var initTime = new Date(this != '' ? this : new Date());
  initTime.setMonth(0); // 本年初始月份
  initTime.setDate(1); // 本年初始时间
  var differenceVal = nowDate - initTime ; // 今天的时间减去本年开始时间，获得相差的时间
  var todayYear = Math.ceil(differenceVal/(2460601000)); // 获取今天是今年第几天
  var index = Math.ceil(todayYear/7); // 获取今天是今年第几周
  return index;
};
// 获取今天是今年的第几天
String.prototype.dateIndexInYear = function () {
  var nowDate = new Date(this != '' ? this : new Date());
  var initTime = new Date(this != '' ? this : new Date());
  initTime.setMonth(0); // 本年初始月份
  initTime.setDate(1); // 本年初始时间
  var differenceVal = nowDate - initTime ; // 今天的时间减去本年开始时间，获得相差的时间
  return Math.ceil(differenceVal/(2460601000));
};
// 获取今天是第几周
String.prototype.weekIndexInMonth = function () {
  var date = new Date(this.trim() != '' ? this : new Date());
  var dateStart = new Date((new Date(this.trim() != '' ? this : new Date()).setDate(1))); // 本月初
  var firstWeek = 1;
  if (dateStart.getDay() === 1) {
    firstWeek = 1;
  } else if (dateStart.getDay() === 0) {
    firstWeek = 8 - 7 + 1;
  } else {
    firstWeek = 8 - dateStart.getDay() + 1;
  }
  var weekIndex = 1;
  var c = date.getDate();
  if (date.getDay() === 1 && date.getDate() < 7) {
    weekIndex = 1;
  } else if (c < firstWeek ) {
    weekIndex = -1;
  } else {
    if (c < 7) {
      weekIndex = Math.ceil(c/7);
    } else {
      c = c - firstWeek + 1;
      if (c%7 === 0) {
        if (dateStart.getDay() !== 6) {
          weekIndex = c/7;
        } else {
          weekIndex = c/7 + 1;
        }
      } else {
        weekIndex = Math.ceil(c/7);
      }
    }
  }
  return weekIndex;
};