Get week of year in JavaScript like in PHP

Question

How do I get the current weeknumber of the year  like PHP s date  W     It should be the ISO-8601 week number of year  weeks starting on Monday

User · Answer

The code snippet which works pretty well for me is this one:

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();

Note:
d is my Date for which I want the current week number.
The + converts the Dates into numbers (working with TypeScript).

User · Answer

Here is my implementation for calculating the week number in JavaScript  corrected for summer and winter time offsets as well   I used the definition of the week from this article  ISO 8601  Weeks are from mondays to sunday  and january 4th is always in the first week of the year      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  amp  amp  this getDate   - currentDotw  gt  28               if true  the week is part of next year          return this getWeekForYear year   1             if  this getMonth      0  amp  amp  this getDate     6 - currentDotw  lt  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       for testing i used the following JavaScript tests in Qunit  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  lt  2020  i              for  month   0  month  lt  12  month                  for  day   1  day  lt  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

User · Answer

I found useful the Java SE s SimpleDateFormat class described on Oracle s specification  http   goo gl 7MbCh5  In my case in Google Apps Script it worked like this   function getWeekNumber       var weekNum   parseInt Utilities formatDate new Date     GMT    w       Logger log weekNum       For example in a spreadsheet macro you can retrieve the actual timezone of the file   function getWeekNumber       var weekNum   parseInt Utilities formatDate new Date    SpreadsheetApp getActiveSpreadsheet   getSpreadsheetTimeZone     w       Logger log weekNum

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This week number thing has been a real pain in the a    Most of scripts around the net didn t work for me  They worked most of time but all of them broke in some point  especially when year changed and last week of the year was suddenly next year s first week etc  Even Angular s date filter showed incorrect data  it was 1st week of next year  angular gave week 53    Note  Examples are designed to work with European weeks  Mon first    getWeek    Date prototype getWeek   function            current week s Thursday     var curWeek   new Date this getTime             curWeek setDay 4           Get year s first week s Thursday     var firstWeek   new Date curWeek getFullYear    0  4           firstWeek setDay 4        return  curWeek getDayIndex   - firstWeek getDayIndex      7   1       setDay          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        I have tested this and it seems to be working very well but if you notice a flaw in it  please let me know

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I tried a lot to get the shortest code to get the weeknumber ISO-conform   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       The variable date is necessary to avoid to alter the original this  I used the return values of setDate   and setMonth   to dispense with getTime   to save code length and I used an expontial number for milliseconds of a day instead of a multiplication of single elements or a number with five zeros  this is Date or Number of milliseconds  return value is String e g   49 2017

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You can use momentjs library also   moment   format  W

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The code below calculates the correct ISO 8601 week number  It matches PHP s date  W   for every week between 1 1 1970 and 1 1 2100          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       Source  Taco van den Broek    If you re not into extending prototypes  then here s a function   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       Sample usage   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

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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

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Shortest workaround for Angular2  DatePipe  adjusted for ISO-8601  import  DatePipe  from  quot  angular common quot    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

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Here is a slight adaptation for Typescript that will also return the dates for the week start and week end  I think it s common to have to display those in a user interface  since people don t usually remember week numbers   x000D   x000D  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    x000D   x000D   x000D

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If you are already in an Angular project you could use  filter  date     For example   var myDate   new Date    var myWeek    filter  date   myDate   ww

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Another library-based option  use d3-time-format  const formatter   d3 timeFormat   U    const weekNum   formatter new Date

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Get the weeknumber of any given Date  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        Example  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

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Not ISO-8601 week number but if the search engine pointed you here anyways  As said above but without a class  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

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You should be able to get what you want here  http   www merlyn demon co uk js-date6 htm YWD   A better link on the same site is  Working with weeks   Edit  Here is some code based on the links provided and that posted eariler by Dommer  It has been lightly tested against results at http   www merlyn demon co uk js-date6 htm YWD  Please test thoroughly  no guarantee provided   Edit 2017  There was an issue with dates during the period that daylight saving was observed and years where 1 Jan was Friday  Fixed by using all UTC methods  The following returns identical results to Moment js    x000D   x000D     For a given date  get the ISO week number x000D     x000D     Based on information at  x000D     x000D        http   www merlyn demon co uk weekcalc htm WNR x000D     x000D     Algorithm is to find nearest thursday  it s year x000D     is the year of the week number  Then get weeks x000D     between that date and the first day of that year  x000D     x000D     Note that dates in one year can be weeks of previous x000D     or next year  overlap is up to 3 days  x000D     x000D     e g  2014 12 29 is Monday in week  1 of 2015 x000D          2012 1 1   is Sunday in week 52 of 2011 x000D      x000D  function getWeekNumber d    x000D         Copy date so don t modify original x000D      d   new Date Date UTC d getFullYear    d getMonth    d getDate      x000D         Set to nearest Thursday  current date   4 - current day number x000D         Make Sunday s day number 7 x000D      d setUTCDate d getUTCDate     4 -  d getUTCDay    7    x000D         Get first day of year x000D      var yearStart   new Date Date UTC d getUTCFullYear   0 1    x000D         Calculate full weeks to nearest Thursday x000D      var weekNo   Math ceil      d - yearStart    86400000    1  7   x000D         Return array of year and week number x000D      return  d getUTCFullYear    weekNo   x000D    x000D   x000D  var result   getWeekNumber new Date     x000D  document write  It  s currently week     result 1      of     result 0    x000D   x000D   x000D    Hours are zeroed when creating the  UTC  date   Minimized  prototype version  returns only week-number     x000D   x000D  Date prototype getWeekNumber   function    x000D    var d   new Date Date UTC this getFullYear    this getMonth    this getDate      x000D    var dayNum   d getUTCDay      7  x000D    d setUTCDate d getUTCDate     4 - dayNum   x000D    var yearStart   new Date Date UTC d getUTCFullYear   0 1    x000D    return Math ceil    d - yearStart    86400000    1  7  x000D     x000D   x000D  document write  The current ISO week number is     new Date   getWeekNumber     x000D   x000D   x000D    Test section  In this section  you can enter any date in YYYY-MM-DD format and check that this code gives the same week number as Moment js ISO week number  tested over 50 years from 2000 to 2050     x000D   x000D  Date prototype getWeekNumber   function    x000D    var d   new Date Date UTC this getFullYear    this getMonth    this getDate      x000D    var dayNum   d getUTCDay      7  x000D    d setUTCDate d getUTCDate     4 - dayNum   x000D    var yearStart   new Date Date UTC d getUTCFullYear   0 1    x000D    return Math ceil    d - yearStart    86400000    1  7  x000D     x000D   x000D  function checkWeek     x000D    var s   document getElementById  dString   value  x000D    var m   moment s   YYYY-MM-DD    x000D    document getElementById  momentWeek   value   m format  W    x000D    document getElementById  answerWeek   value   m toDate   getWeekNumber          x000D    x000D   lt script src  https   cdnjs cloudflare com ajax libs moment js 2 18 1 moment min js  gt  lt  script gt  x000D   x000D  Enter date  YYYY-MM-DD   lt input id  dString  value  2021-02-22  gt  x000D   lt button onclick  checkWeek this   gt Check week number lt  button gt  lt br gt  x000D  Moment   lt input id  momentWeek  readonly gt  lt br gt  x000D  Answer   lt input id  answerWeek  readonly gt  x000D   x000D   x000D

User · Answer

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

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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          Following code is timezone-independent  UTC dates used  and works according to the https   en wikipedia org wiki ISO 8601

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With Luxon  https   github com moment luxon      import   DateTime   from  luxon   const week  number   DateTime fromJSDate new Date    weekNumber

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Jacob Wright s Date format   library implements date formatting in the style of PHP s date   function and supports the ISO-8601 week number   new Date   format  W      It may be a bit overkill for just a week number  but it does support PHP style formatting and is quite handy if you ll be doing a lot of this

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This adds  getWeek  method to Date prototype which returns number of week from the beginning of the year  The argument defines which day of the week to consider the first  If no argument passed  first day is assumed Sunday          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  amp  amp   typeof weekStart      number     weekStart   1     0    weekStart  lt  0    weekStart  gt  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

[javascript] Get week of year in JavaScript like in PHP

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