给定月份和年份，确定该月的第三个星期五

Question

给定一个年份和月份，我想确定该月的第三个星期五的日期。我如何利用moment.js来确定这个呢?

。October 2015 => 16th October 2015

Answer 1

给定年和月为整数，并假设星期五是您所在地区一周的第五天(星期一是一周的第一天)，则可以有:

function getThirdFriday(year, month){
    // Convert date to moment (month 0-11)
    var myMonth = moment({year: year, month: month});
    // Get first Friday of the first week of the month
    var firstFriday = myMonth.weekday(4);
    var nWeeks = 2;
    // Check if first Friday is in the given month
    if( firstFriday.month() != month ){
        nWeeks++;
    }
    // Return 3rd Friday of the month formatted (custom format)
    return firstFriday.add(nWeeks, 'weeks').format("DD MMMM YYYY");
}

如果您将月和年作为字符串，则可以使用时刻解析函数而不是Object表示法，因此您将有:

var myMonth = moment("October 2015", "MMMM yyyy");

如果星期五不是一周的第五天(索引为4的天)，您可以使用moment.weekdays()

Answer 2

根据上面(1和2)的答案，

我对函数进行了一般化，使其可以返回任何给定日期的任何工作日或任何星期。

var getNthWeekday = function(baseDate, weekth, weekday){
    // parse base date
    var date = moment(baseDate);
    var year = date.year();
    var month = date.month();
    // Convert date to moment (month 0-11)
    var myMonth = moment({year: year, month: month});
    // assume we won't have to move forward any number of weeks
    var weeksToAdvance = weekth-1;
    // Get first weekday of the first week of the month
    var firstOccurranceOfDay = myMonth.weekday(weekday);
    // Check if first weekday occurrance is in the given month
    if( firstOccurranceOfDay.month() != month ){
        weeksToAdvance++;
    }
    // Return nth weekday of month formatted (custom format)
    return firstOccurranceOfDay.add(weeksToAdvance, 'weeks');
}

Answer 3

基于@VincenzoC.

这允许我发送和接收一个瞬间。

let getThirdFriday: function(mDate) {
  // Based on https://stackoverflow.com/a/34278588
  // By default we will need to add two weeks to the first friday
  let nWeeks = 2,
  month = mDate.month();
  // Get first Friday of the first week of the month
  mDate = mDate.date(1).day(5);
  // Check if first Friday is in the given month
  //  it may have gone to the previous month
  if (mDate.month() != month) {
    nWeeks++;
  }
  // Return 3rd Friday of the month formatted (custom format)
  return mDate.add(nWeeks, 'weeks');
}

那么我可以这样命名它:

let threeMonth = getThirdFriday(
                                  moment()
                                  .add(3, 'months')
                         ).format("YYYY-MM-DD");