像在 PHP 中一样在 JavaScript 中获取一年中的一周

你应该能够在这里得到你想要的东西：http://www.merlyn.demon.co.uk/js-date6.htm#YWD。

同一网站上更好的链接是：使用周。

编辑

以下是一些基于提供的链接的代码，以及Dommer发布的eariler。它已经根据 http://www.merlyn.demon.co.uk/js-date6.htm#YWD 的结果进行了轻微的测试。请彻底测试，不提供任何保证。

编辑 2017

在遵守夏令时的期间以及 1 月 1 日是星期五的年份中存在日期问题。通过使用所有 UTC 方法修复。以下内容返回与 Moment.js 相同的结果。

/* For a given date, get the ISO week number
 *
 * Based on information at:
 *
 *    THIS PAGE (DOMAIN EVEN) DOESN'T EXIST ANYMORE UNFORTUNATELY
 *    http://www.merlyn.demon.co.uk/weekcalc.htm#WNR
 *
 * Algorithm is to find nearest thursday, it's year
 * is the year of the week number. Then get weeks
 * between that date and the first day of that year.
 *
 * Note that dates in one year can be weeks of previous
 * or next year, overlap is up to 3 days.
 *
 * e.g. 2014/12/29 is Monday in week  1 of 2015
 *      2012/1/1   is Sunday in week 52 of 2011
 */
function getWeekNumber(d) {
    // Copy date so don't modify original
    d = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
    // Set to nearest Thursday: current date + 4 - current day number
    // Make Sunday's day number 7
    d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay()||7));
    // Get first day of year
    var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1));
    // Calculate full weeks to nearest Thursday
    var weekNo = Math.ceil(( ( (d - yearStart) / 86400000) + 1)/7);
    // Return array of year and week number
    return [d.getUTCFullYear(), weekNo];
}
var result = getWeekNumber(new Date());
document.write('It''s currently week ' + result[1] + ' of ' + result[0]);

创建"UTC"日期时，小时数为零。

最小化的原型版本(仅返回周数(：

Date.prototype.getWeekNumber = function(){
  var d = new Date(Date.UTC(this.getFullYear(), this.getMonth(), this.getDate()));
  var dayNum = d.getUTCDay() || 7;
  d.setUTCDate(d.getUTCDate() + 4 - dayNum);
  var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1));
  return Math.ceil((((d - yearStart) / 86400000) + 1)/7)
};
document.write('The current ISO week number is ' + new Date().getWeekNumber());

测试部分

在本节中，您可以输入 YYYY-MM-DD 格式的任何日期，并检查此代码是否提供与 Moment.js ISO 周数相同的周数(从 2000 年到 2050 年经过 50 年的测试(。

Date.prototype.getWeekNumber = function(){
  var d = new Date(Date.UTC(this.getFullYear(), this.getMonth(), this.getDate()));
  var dayNum = d.getUTCDay() || 7;
  d.setUTCDate(d.getUTCDate() + 4 - dayNum);
  var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1));
  return Math.ceil((((d - yearStart) / 86400000) + 1)/7)
};
function checkWeek() {
  var s = document.getElementById('dString').value;
  var m = moment(s, 'YYYY-MM-DD');
  document.getElementById('momentWeek').value = m.format('W');
  document.getElementById('answerWeek').value = m.toDate().getWeekNumber();      
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
Enter date  YYYY-MM-DD: <input id="dString" value="2021-02-22">
<button onclick="checkWeek(this)">Check week number</button><br>
Moment: <input id="momentWeek" readonly><br>
Answer: <input id="answerswerWeek" readonly>

你也可以使用 momentjs 库：

moment().format('W')

不是 ISO-8601 周号，但如果搜索引擎无论如何都指向你这里。

如上所述，但没有类：

let now = new Date();
let onejan = new Date(now.getFullYear(), 0, 1);
let week = Math.ceil((((now.getTime() - onejan.getTime()) / 86400000) + onejan.getDay() + 1) / 7);
console.log(week);

Accordily http://javascript.about.com/library/blweekyear.htm

Date.prototype.getWeek = function() {
  var onejan = new Date(this.getFullYear(), 0, 1);
  var millisecsInDay = 86400000;
  return Math.ceil((((this - onejan) / millisecsInDay) + onejan.getDay() + 1) / 7);
};
let d = new Date(2020,11,30);
for (let i=0; i<14; i++) {
  console.log(`${d.toDateString()} is week ${d.getWeek()}`);
  d.setDate(d.getDate() + 1);
}

下面的代码计算出正确的ISO 8601周数。它与 PHP 在 1970 年 1 月 1 日至 2100 年 1 月 1 日之间每周的date("W")相匹配。

/**
 * Get the ISO week date week number
 */
Date.prototype.getWeek = function () {
  // Create a copy of this date object
  var target = new Date(this.valueOf());
  // ISO week date weeks start on Monday, so correct the day number
  var dayNr = (this.getDay() + 6) % 7;
  // ISO 8601 states that week 1 is the week with the first Thursday of that year
  // Set the target date to the Thursday in the target week
  target.setDate(target.getDate() - dayNr + 3);
  // Store the millisecond value of the target date
  var firstThursday = target.valueOf();
  // Set the target to the first Thursday of the year
  // First, set the target to January 1st
  target.setMonth(0, 1);
  // Not a Thursday? Correct the date to the next Thursday
  if (target.getDay() !== 4) {
    target.setMonth(0, 1 + ((4 - target.getDay()) + 7) % 7);
  }
  // The week number is the number of weeks between the first Thursday of the year
  // and the Thursday in the target week (604800000 = 7 * 24 * 3600 * 1000)
  return 1 + Math.ceil((firstThursday - target) / 604800000);
}

来源： Taco van den Broek

如果您不喜欢扩展原型，那么这里有一个函数：

function getWeek(date) {
  if (!(date instanceof Date)) date = new Date();
  // ISO week date weeks start on Monday, so correct the day number
  var nDay = (date.getDay() + 6) % 7;
  // ISO 8601 states that week 1 is the week with the first Thursday of that year
  // Set the target date to the Thursday in the target week
  date.setDate(date.getDate() - nDay + 3);
  // Store the millisecond value of the target date
  var n1stThursday = date.valueOf();
  // Set the target to the first Thursday of the year
  // First, set the target to January 1st
  date.setMonth(0, 1);
  // Not a Thursday? Correct the date to the next Thursday
  if (date.getDay() !== 4) {
    date.setMonth(0, 1 + ((4 - date.getDay()) + 7) % 7);
  }
  // The week number is the number of weeks between the first Thursday of the year
  // and the Thursday in the target week (604800000 = 7 * 24 * 3600 * 1000)
  return 1 + Math.ceil((n1stThursday - date) / 604800000);
}

示例用法：

getWeek(); // Returns 37 (or whatever the current week is)
getWeek(new Date('Jan 2, 2011')); // Returns 52
getWeek(new Date('Jan 1, 2016')); // Returns 53
getWeek(new Date('Jan 4, 2016')); // Returns 1

Jacob Wright 的Date.format()库以 PHP 的 date() 函数风格实现日期格式，并支持 ISO-8601 周数：

new Date().format('W');

对于一个星期的数字来说，这可能有点矫枉过正，但它确实支持 PHP 样式格式，如果你要做很多这样的事情，它会非常方便。

getWeekOfYear: function(date) {
        var target = new Date(date.valueOf()),
            dayNumber = (date.getUTCDay() + 6) % 7,
            firstThursday;
        target.setUTCDate(target.getUTCDate() - dayNumber + 3);
        firstThursday = target.valueOf();
        target.setUTCMonth(0, 1);
        if (target.getUTCDay() !== 4) {
            target.setUTCMonth(0, 1 + ((4 - target.getUTCDay()) + 7) % 7);
        }
        return Math.ceil((firstThursday - target) /  (7 * 24 * 3600 * 1000)) + 1;
    }

以下代码与时区无关(使用的 UTC 日期(，并根据 https://en.wikipedia.org/wiki/ISO_8601

获取任何给定日期的周数

function week(year,month,day) {
    function serial(days) { return 86400000*days; }
    function dateserial(year,month,day) { return (new Date(year,month-1,day).valueOf()); }
    function weekday(date) { return (new Date(date)).getDay()+1; }
    function yearserial(date) { return (new Date(date)).getFullYear(); }
    var date = year instanceof Date ? year.valueOf() : typeof year === "string" ? new Date(year).valueOf() : dateserial(year,month,day), 
        date2 = dateserial(yearserial(date - serial(weekday(date-serial(1))) + serial(4)),1,3);
    return ~~((date - date2 + serial(weekday(date2) + 5))/ serial(7));
}

例

console.log(
    week(2016, 06, 11),//23
    week(2015, 9, 26),//39
    week(2016, 1, 1),//53
    week(2016, 1, 4),//1
    week(new Date(2016, 0, 4)),//1
    week("11 january 2016")//2
);

我发现Java SE的SimpleDateFormat类在Oracle的规范中描述很有用：http://goo.gl/7MbCh5。在我的情况下，在谷歌应用脚本中，它的工作原理是这样的：

function getWeekNumber() {
  var weekNum = parseInt(Utilities.formatDate(new Date(), "GMT", "w"));
  Logger.log(weekNum);
}

例如，在电子表格宏中，您可以检索文件的实际时区：

function getWeekNumber() {
  var weekNum = parseInt(Utilities.formatDate(new Date(), SpreadsheetApp.getActiveSpreadsheet().getSpreadsheetTimeZone(), "w"));
  Logger.log(weekNum);
}

这会将"getWeek"方法添加到 Date.prototype，该方法返回年初的周数。该参数定义在一周中的哪一天考虑第一天。如果没有通过争论，则假定第一天为星期日。

/**
 * Get week number in the year.
 * @param  {Integer} [weekStart=0]  First day of the week. 0-based. 0 for Sunday, 6 for Saturday.
 * @return {Integer}                0-based number of week.
 */
Date.prototype.getWeek = function(weekStart) {
    var januaryFirst = new Date(this.getFullYear(), 0, 1);
    if(weekStart !== undefined && (typeof weekStart !== 'number' || weekStart % 1 !== 0 || weekStart < 0 || weekStart > 6)) {
      throw new Error('Wrong argument. Must be an integer between 0 and 6.');
    }
    weekStart = weekStart || 0;
    return Math.floor((((this - januaryFirst) / 86400000) + januaryFirst.getDay() - weekStart) / 7);
};

如果您已经在 Angular 项目中，您可以使用 $filter('date') .

例如：

var myDate = new Date();
var myWeek = $filter('date')(myDate, 'ww');

对我来说效果很好的代码片段是这个：

var yearStart = +new Date(d.getFullYear(), 0, 1);
var today = +new Date(d.getFullYear(),d.getMonth(),d.getDate());
var dayOfYear = ((today - yearStart + 1) / 86400000);
return Math.ceil(dayOfYear / 7).toString();

注意：
d是我想要当前周数的日期。
+将日期转换为数字(使用 TypeScript(。

与 Luxon (https://github.com/moment/luxon( ：

import { DateTime } from 'luxon';
const week: number = DateTime.fromJSDate(new Date()).weekNumber;

本周的数字事件在a**中真的很痛苦。网络上大多数琐碎的解决方案对我来说并不真正有效，因为它们大部分时间都在工作，但它们都在某个时候崩溃了，尤其是当年份发生变化并且一年的最后一周突然成为明年的第一周等时。甚至 Angular 的日期过滤器也显示了不正确的数据(这是明年的第一周，Angular 给出了第 53 周(。

注意：这些示例旨在与欧洲周(周一优先(一起使用！

getWeek((

Date.prototype.getWeek = function(){
    // current week's Thursday
    var curWeek = new Date(this.getTime());
        curWeek.setDay(4);
    // current year's first week's Thursday
    var firstWeek = new Date(curWeek.getFullYear(), 0, 4);
        firstWeek.setDay(4);
    return (curWeek.getDayIndex() - firstWeek.getDayIndex()) / 7 + 1;
};

设置日((

/**
* Make a setDay() prototype for Date
* Sets week day for the date
*/
Date.prototype.setDay = function(day){
    // Get day and make Sunday to 7
    var weekDay = this.getDay() || 7;
    var distance = day - weekDay;
    this.setDate(this.getDate() + distance);
    return this;
}

getDayIndex((

/*
* Returns index of given date (from Jan 1st)
*/
Date.prototype.getDayIndex = function(){
    var start = new Date(this.getFullYear(), 0, 0);
    var diff = this - start;
    var oneDay = 86400000;
    
    return Math.floor(diff / oneDay);
};

我已经对此进行了测试，它似乎运行良好，但是如果您发现其中的缺陷，请告诉我。

此代码修复了 nvd 回答中的错误

function getWeek(param) {
    let onejan = new Date(param.getFullYear(), 0, 1);
    return Math.ceil((((param.getTime() - onejan.getTime()) / 86400000) + onejan.getDay()) / 7);
}

这是我在 JavaScript 中计算周数的实现。 还针对夏令时和冬令时偏移进行了校正。我使用了本文中一周的定义：ISO 8601

是从星期一到星期日，1月4日总是在一年的第一周。

// add get week prototype functions
// weeks always start from monday to sunday
// january 4th is always in the first week of the year
Date.prototype.getWeek = function () {
    year = this.getFullYear();
    var currentDotw = this.getWeekDay();
    if (this.getMonth() == 11 && this.getDate() - currentDotw > 28) {
        // if true, the week is part of next year 
        return this.getWeekForYear(year + 1);
    }
    if (this.getMonth() == 0 && this.getDate() + 6 - currentDotw < 4) {
        // if true, the week is part of previous year
        return this.getWeekForYear(year - 1);
    }
    return this.getWeekForYear(year);
}
// returns a zero based day, where monday = 0
// all weeks start with monday
Date.prototype.getWeekDay = function () {
    return  (this.getDay() + 6) % 7;
}
// corrected for summer/winter time
Date.prototype.getWeekForYear = function (year) {
    var currentDotw = this.getWeekDay();
    var fourjan = new Date(year, 0, 4);
    var firstDotw = fourjan.getWeekDay();
    var dayTotal = this.getDaysDifferenceCorrected(fourjan) // the difference in days between the two dates.
    // correct for the days of the week
    dayTotal += firstDotw; // the difference between the current date and the first monday of the first week, 
    dayTotal -= currentDotw; // the difference between the first monday and the current week's monday
    // day total should be a multiple of 7 now
    var weeknumber = dayTotal / 7 + 1; // add one since it gives a zero based week number.
    return weeknumber;
}
// corrected for timezones and offset
Date.prototype.getDaysDifferenceCorrected = function (other) {
    var millisecondsDifference = (this - other);
    // correct for offset difference. offsets are in minutes, the difference is in milliseconds
    millisecondsDifference += (other.getTimezoneOffset()- this.getTimezoneOffset()) * 60000;
    // return day total. 1 day is 86400000 milliseconds, floor the value to return only full days
    return Math.floor(millisecondsDifference / 86400000);
}

为了进行测试，我在Qunit中使用了以下JavaScript测试

var runweekcompare = function(result, expected) {
    equal(result, expected,'Week nr expected value: ' + expected + ' Actual value: ' + result);
}
test('first week number test', function () {
    expect(5);
    var temp = new Date(2016, 0, 4); // is the monday of the first week of the year
    runweekcompare(temp.getWeek(), 1);
    var temp = new Date(2016, 0, 4, 23, 50); // is the monday of the first week of the year
    runweekcompare(temp.getWeek(), 1);
    var temp = new Date(2016, 0, 10, 23, 50); // is the sunday of the first week of the year
    runweekcompare(temp.getWeek(), 1);
    var temp = new Date(2016, 0, 11, 23, 50); // is the second week of the year
    runweekcompare(temp.getWeek(), 2);
    var temp = new Date(2016, 1, 29, 23, 50); // is the 9th week of the year
    runweekcompare(temp.getWeek(), 9);
});
test('first day is part of last years last week', function () {
    expect(2);
    var temp = new Date(2016, 0, 1, 23, 50); // is the first last week of the previous year
    runweekcompare(temp.getWeek(), 53);
    var temp = new Date(2011, 0, 2, 23, 50); // is the first last week of the previous year
    runweekcompare(temp.getWeek(), 52);
});
test('last  day is part of next years first week', function () {
    var temp = new Date(2013, 11, 30); // is part of the first week of 2014
    runweekcompare(temp.getWeek(), 1);
});
test('summer winter time change', function () {
    expect(2);
    var temp = new Date(2000, 2, 26); 
    runweekcompare(temp.getWeek(), 12);
    var temp = new Date(2000, 2, 27); 
    runweekcompare(temp.getWeek(), 13);
});
test('full 20 year test', function () {
    //expect(20 * 12 * 28 * 2);
    for (i = 2000; i < 2020; i++) {
        for (month = 0; month < 12; month++) {
            for (day = 1; day < 29 ; day++) {
                var temp = new Date(i, month, day);
                var expectedweek = temp.getWeek();
                var temp2 = new Date(i, month, day, 23, 50);
                var resultweek = temp.getWeek();
                equal(expectedweek, Math.round(expectedweek), 'week number whole number expected ' + Math.round(expectedweek) + ' resulted week nr ' + expectedweek);
                equal(resultweek, expectedweek, 'Week nr expected value: ' + expectedweek + ' Actual value: ' + resultweek + ' for year ' + i + ' month ' + month + ' day ' + day);
            }
        }
    }
});

这是对 Typescript 的轻微调整，它还将返回一周开始和结束的日期。我认为必须在用户界面中显示这些是很常见的，因为人们通常不记得周数。

function getWeekNumber(d: Date) {
  // Copy date so don't modify original
  d = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
  // Set to nearest Thursday: current date + 4 - current day number Make
  // Sunday's day number 7
  d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay() || 7));
  // Get first day of year
  const yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
  // Calculate full weeks to nearest Thursday
  const weekNo = Math.ceil(
    ((d.getTime() - yearStart.getTime()) / 86400000 + 1) / 7
  );
  const weekStartDate = new Date(d.getTime());
  weekStartDate.setUTCDate(weekStartDate.getUTCDate() - 3);
  const weekEndDate = new Date(d.getTime());
  weekEndDate.setUTCDate(weekEndDate.getUTCDate() + 3);
  return [d.getUTCFullYear(), weekNo, weekStartDate, weekEndDate] as const;
}

针对某些日期测试的打字稿实现。此实现允许您将一周的第一天设置为任何一天。

//sunday = 0, monday = 1, ...
static getWeekNumber(date: Date, firstDay = 1): number {
  const d = new Date(date.getTime());
  d.setHours(0, 0, 0, 0);
  //Set to first day of the week since it is the same weeknumber
  while(d.getDay() != firstDay){
    d.setDate(d.getDate() - 1);
  }
  const dayOfYear = this.getDayOfYear(d);
  let weken = Math.floor(dayOfYear/7);
  // add an extra week if 4 or more days are in this year.
  const daysBefore = ((dayOfYear % 7) - 1);
  if(daysBefore >= 4){
    weken += 1;
  }
  //if the last 3 days onf the year,it is the first week
  const t = new Date(d.getTime());
  t.setDate(t.getDate() + 3);
  if(t.getFullYear() > d.getFullYear()){
    return 1;
  }
  weken += 1;
  return weken;
}
private static getDayOfYear(date: Date){
  const start = new Date(date.getFullYear(), 0, 0);
  const diff = (date.getTime() - start.getTime()) + ((start.getTimezoneOffset() - date.getTimezoneOffset()) * 60 * 1000);
  const oneDay = 1000 * 60 * 60 * 24;
  const day = Math.floor(diff / oneDay);
  return day;
}

测试：

describe('getWeeknumber', () => {
  it('should be ok for 0 sunday', () => {
    expect(DateUtils.getWeekNumber(new Date(2015, 0, 4), 0)).toBe(1);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 1), 0)).toBe(1);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 2), 0)).toBe(1);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 8), 0)).toBe(2);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 9), 0)).toBe(2);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 28), 0)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 29), 0)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 30), 0)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 31), 0)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2022, 0, 3), 0)).toBe(1);
  });
  it('should be ok for monday 1 default', () => {
    expect(DateUtils.getWeekNumber(new Date(2015, 0, 4), 1)).toBe(1);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 1), 1)).toBe(52);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 2), 1)).toBe(1);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 8), 1)).toBe(1);
    expect(DateUtils.getWeekNumber(new Date(2017, 0, 9), 1)).toBe(2);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 28), 1)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 29), 1)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 30), 1)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2020, 11, 31), 1)).toBe(53);
    expect(DateUtils.getWeekNumber(new Date(2022, 0, 3), 1)).toBe(1);
  });
});

我尝试了很多方法来获取最短的代码来获得周数 ISO 一致性。

Date.prototype.getWeek=function(){
    var date=new Date(this);
    date.setHours(0,0,0,0);
    return Math.round(((date.setDate(this.getDate()+2-(this.getDay()||7))-date.setMonth(0,4))/8.64e7+3+(date.getDay()||7))/7)+"/"+date.getFullYear();}

变量date是必要的，以避免更改原始this。我使用 setDate() 和 setMonth() 的返回值来省去getTime()以节省代码长度，并且我使用一天毫秒的 expontial 数字，而不是单个元素的乘法或带有五个零的数字。 this为日期或毫秒数，则返回值为String例如"49/2017"。

另一个基于库的选项：使用 d3-time-format ：

const formatter = d3.timeFormat('%U');
const weekNum = formatter(new Date());

Angular2+ DatePipe的最短解决方法，针对ISO-8601进行了调整：

import {DatePipe} from "@angular/common";
public rightWeekNum: number = 0;
  
constructor(private datePipe: DatePipe) { }
    
calcWeekOfTheYear(dateInput: Date) {
  let falseWeekNum = parseInt(this.datePipe.transform(dateInput, 'ww'));
  this.rightWeekNum = (dateInput.getDay() == 0) ? falseWeekNumber-1 : falseWeekNumber;
}

灵感来自RobG的回答。

我想要的是给定日期的星期几。所以我的答案只是基于星期天。但是您可以选择其他日期(即星期一，星期二...

首先，我找到给定日期的星期日，然后计算一周。

function getStartWeekDate(d = null) {
  const now = d || new Date();
  now.setHours(0, 0, 0, 0);
  const sunday = new Date(now);
  sunday.setDate(sunday.getDate() - sunday.getDay());
  return sunday;
}
function getWeek(date) {
  const sunday = getStartWeekDate(date);
  const yearStart = new Date(Date.UTC(2021, 0, 1));
  const weekNo = Math.ceil((((sunday - yearStart) / 86400000) + 1) / 7);
  return weekNo;
}
// tests
for (let i = 0; i < 7; i++)  {
  let m = 14 + i;
  let x = getWeek(new Date(2021, 2, m));
  console.log('week num: ' + x, x + ' == ' + 11, x == 11, m);
}
for (let i = 0; i < 7; i++)  {
  let m = 21 + i;
  let x = getWeek(new Date(2021, 2, m));
  console.log('week num: ' + x, x + ' == ' + 12, x == 12, 'date day: ' +  m);
}
for (let i = 0; i < 4; i++)  {
  let m = 28 + i;
  let x = getWeek(new Date(2021, 2, m));
  console.log('week num: ' + x, x + ' == ' + 13, x == 13, 'date day: ' + m);
}
for (let i = 0; i < 3; i++)  {
  let m = 1 + i;
  let x = getWeek(new Date(2021, 3, m));
  console.log('week num: ' + x, x + ' == ' + 13, x == 13, 'date day: ' +  m);
}
for (let i = 0; i < 7; i++)  {
  let m = 4 + i;
  let x = getWeek(new Date(2021, 3, m));
  console.log('week num: ' + x, x + ' == ' + 14, x == 14, 'date day: ' +  m);
}

import dayJs from 'dayjs';
import isoWeek from 'dayjs/plugin/isoWeek';
dayJs.extend(isoWeek);
/**
 * Get the current week number based on date.
 *
 * @return {number}
 * @param date
 */
export const getWeekNumberByDate = (date) => dayJs(date).isoWeek();

now = new Date();
today = new Date(now.getFullYear(), now.getMonth(), now.getDate());
firstOfYear = new Date(now.getFullYear(), 0, 1);
numOfWeek = Math.ceil((((today - firstOfYear) / 86400000)-1)/7);