如何計算僅給定月份、該月內的周數和星期幾的日期

Question

我正在調用一個返回以下對象的 api，告訴我夏令時從 3 月 11 日開始，適用於給定的時區：

{
  dayOfWeek: "Sunday",
  month: 3,
  timeOfDay: "0001-01-01T02:00:00.000Z",
  week: 2
}

在這種情況下，week:2 代表三月的第二周。

我如何從中創建 3 月 11 日？ 我有以下功能在 3 月份運行良好，但意識到如果說 api 返回以下內容，這將在 4 月份失敗：

{
  dayOfWeek: "Saturday",
  month: 4,
  timeOfDay: "0001-01-01T02:00:00.000Z",
  week: 2
}

代碼：

/**
 * Given the year, month, week day, week number of the month, and time, calculate a date
    - set the date to the first day of the month
    - then adjust the date backwards to the proper weekday
    - then move it forward by 7 * week number to get it to the proper date
 */
calcDateFromDaylightSavingRulesAPI: function(year, month, time, dayOfWeek, weekNum) {
    const weekDays = {
        Sunday: 0,
        Monday: 1,
        Tuesday: 2,
        Wednesday: 3,
        Thursday: 4,
        Friday: 5,
        Saturday: 6
    };

    const date = new Date(year, month, 1, time);
    date.setDate(date.getDate() + weekDays[dayOfWeek] - date.getDay());
    date.setDate(date.getDate() + (weekNum * constants.DAYS_PER_WEEK));

    return date;

Answer 1

如果您只想要一個月中某個特定日期的第 n 次出現，您可以獲取該月的第 1 次，移至該特定日期的第一次出現，然后添加(n-1) * 7天以獲得第 n 次出現，例如

 function getNthDay(year, month, dayName, n) { var weekDays = { Sunday: 0, Monday: 1, Tuesday: 2, Wednesday: 3, Thursday: 4, Friday: 5, Saturday: 6 }; // validate input values here, throw errors if required, eg // dayName must be in weekdays, 0 < n < 6 // Create date for first day of required month var d = new Date(year, month - 1, 1); // Set to first instance of particular day d.setDate((8 - (d.getDay() - weekDays[dayName]))%7); // Add (n-1)*7 days d.setDate(d.getDate() + (n-1) * 7); // Check final date is still in required month return d.getMonth() == month - 1? d : 'fail'; } // Second Sunday in March, 2018 console.log(getNthDay(2018,3,'Sunday',2).toString())

如果您想要第二周的星期日，則計算起來有點困難，因為有些地方從星期日開始，有些地方從星期一開始。 此外，一個月中一周的算法可能會因地而異（就像一年中的一周一樣）。

Answer 2

我認為這現在工作正常。 謝謝大家的幫助！

/**
 * Given an object which contains month, time, week day, and week number in a month, calculate a date
    - set the date to the first day of the month
    - then adjust the date backwards to the proper weekday
    - then move it forward by 7 * week number to get it to the proper date
 */
calcDateFromDaylightSavingRulesAPI: function(ruleSet) {
    const today = new Date();
    const year = today.getFullYear();
    const month = ruleSet.month - 1;
    const time = new Date(ruleSet.timeOfDay).getUTCHours();
    const dayOfWeek = ruleSet.dayOfWeek;
    const weekNum = ruleSet.week;

    const weekDays = {
        Sunday: 0,
        Monday: 1,
        Tuesday: 2,
        Wednesday: 3,
        Thursday: 4,
        Friday: 5,
        Saturday: 6
    };

    const date = new Date(year, month, 1, time);
    const diff = weekDays[dayOfWeek] - date.getDay();
    date.setDate(date.getDate() + (diff >= 0 ? diff - 7 : diff));
    date.setDate(date.getDate() + (weekNum * constants.DAYS_PER_WEEK));

    return date;
},