Get Weeks In Month Through Javascript

In Javascript, how do I get the number of weeks in a month? I can't seem to find code for this anywhere.

I need this to 开发者_JS百科be able to know how many rows I need for a given month.

To be more specific, I would like the number of weeks that have at least one day in the week (a week being defined as starting on Sunday and ending on Saturday).

So, for something like this, I would want to know it has 5 weeks:

S  M  T  W  R  F  S

         1  2  3  4

5  6  7  8  9  10 11

12 13 14 15 16 17 18

19 20 21 22 23 24 25

26 27 28 29 30 31 

Thanks for all the help.

---

Weeks start on Sunday

This ought to work even when February doesn't start on Sunday.

function weekCount(year, month_number) {

    // month_number is in the range 1..12

    var firstOfMonth = new Date(year, month_number-1, 1);
    var lastOfMonth = new Date(year, month_number, 0);

    var used = firstOfMonth.getDay() + lastOfMonth.getDate();

    return Math.ceil( used / 7);
}

Weeks start on Monday

function weekCount(year, month_number) {

    // month_number is in the range 1..12

    var firstOfMonth = new Date(year, month_number-1, 1);
    var lastOfMonth = new Date(year, month_number, 0);

    var used = firstOfMonth.getDay() + 6 + lastOfMonth.getDate();

    return Math.ceil( used / 7);
}

Weeks start another day

function weekCount(year, month_number, startDayOfWeek) {
  // month_number is in the range 1..12

  // Get the first day of week week day (0: Sunday, 1: Monday, ...)
  var firstDayOfWeek = startDayOfWeek || 0;

  var firstOfMonth = new Date(year, month_number-1, 1);
  var lastOfMonth = new Date(year, month_number, 0);
  var numberOfDaysInMonth = lastOfMonth.getDate();
  var firstWeekDay = (firstOfMonth.getDay() - firstDayOfWeek + 7) % 7;

  var used = firstWeekDay + numberOfDaysInMonth;

  return Math.ceil( used / 7);
}

---

None of the solutions proposed here don't works correctly, so I wrote my own variant and it works for any cases.

Simple and working solution:

/**
 * Returns count of weeks for year and month
 *
 * @param {Number} year - full year (2016)
 * @param {Number} month_number - month_number is in the range 1..12
 * @returns {number}
 */
var weeksCount = function(year, month_number) {
    var firstOfMonth = new Date(year, month_number - 1, 1);
    var day = firstOfMonth.getDay() || 6;
    day = day === 1 ? 0 : day;
    if (day) { day-- }
    var diff = 7 - day;
    var lastOfMonth = new Date(year, month_number, 0);
    var lastDate = lastOfMonth.getDate();
    if (lastOfMonth.getDay() === 1) {
        diff--;
    }
    var result = Math.ceil((lastDate - diff) / 7);
    return result + 1;
};

you can try it here

---

This is very simple two line code. and i have tested 100%.

Date.prototype.getWeekOfMonth = function () {
    var firstDay = new Date(this.setDate(1)).getDay();
    var totalDays = new Date(this.getFullYear(), this.getMonth() + 1, 0).getDate();
    return Math.ceil((firstDay + totalDays) / 7);
}

How to use

var totalWeeks = new Date().getWeekOfMonth();
console.log('Total Weeks in the Month are : + totalWeeks ); 

---

You'll have to calculate it.

You can do something like

var firstDay = new Date(2010, 0, 1).getDay(); // get the weekday january starts on
var numWeeks = 5 + (firstDay >= 5 ? 1 : 0); // if the months starts on friday, then it will end on sunday

Now we just need to genericize it.

var dayThreshold = [ 5, 1, 5, 6, 5, 6, 5, 5, 6, 5, 6, 5 ];
function GetNumWeeks(month, year)
{
    var firstDay = new Date(year, month, 1).getDay();
    var baseWeeks = (month == 1 ? 4 : 5); // only February can fit in 4 weeks
    // TODO: account for leap years
    return baseWeeks + (firstDay >= dayThreshold[month] ? 1 : 0); // add an extra week if the month starts beyond the threshold day.
}

Note: When calling, remember that months are zero indexed in javascript (i.e. January == 0).

---

function weeksinMonth(m, y){
 y= y || new Date().getFullYear();
 var d= new Date(y, m, 0);
 return Math.floor((d.getDate()- 1)/7)+ 1;     
}
alert(weeksinMonth(3))

// the month range for this method is 1 (january)-12(december)

---

The most easy to understand way is

<div id="demo"></div>

<script type="text/javascript">

 function numberOfDays(year, month)
 {
   var d = new Date(year, month, 0);
   return d.getDate();
 }


 function getMonthWeeks(year, month_number)
 {
   var $num_of_days       = numberOfDays(year, month_number)
    ,  $num_of_weeks      = 0
    ,  $start_day_of_week = 0; 

   for(i=1; i<=$num_of_days; i++)
   {
      var $day_of_week = new Date(year, month_number, i).getDay();
      if($day_of_week==$start_day_of_week)
      {
        $num_of_weeks++;
      }   
   }

    return $num_of_weeks;
 }

   var d = new Date()
      , m = d.getMonth()
      , y = d.getFullYear();

   document.getElementById('demo').innerHTML = getMonthWeeks(y, m);
</script>

---

using moment js

function getWeeksInMonth(year, month){

        var monthStart     = moment().year(year).month(month).date(1);
        var monthEnd       = moment().year(year).month(month).endOf('month');
        var numDaysInMonth = moment().year(year).month(month).endOf('month').date();

        //calculate weeks in given month
        var weeks      = Math.ceil((numDaysInMonth + monthStart.day()) / 7);
        var weekRange  = [];
        var weekStart = moment().year(year).month(month).date(1);
        var i=0;

        while(i<weeks){
            var weekEnd   = moment(weekStart);


            if(weekEnd.endOf('week').date() <= numDaysInMonth && weekEnd.month() == month) {
                weekEnd = weekEnd.endOf('week').format('LL');
            }else{
                weekEnd = moment(monthEnd);
                weekEnd = weekEnd.format('LL')
            }

            weekRange.push({
                'weekStart': weekStart.format('LL'),
                'weekEnd': weekEnd
            });


            weekStart = weekStart.weekday(7);
            i++;
        }

        return weekRange;
    } console.log(getWeeksInMonth(2016, 7))

---

ES6 variant, using consistent zero-based months index. Tested for years from 2015 to 2025.

/**
 * Returns number of weeks
 *
 * @param {Number} year - full year (2018)
 * @param {Number} month - zero-based month index (0-11)
 * @param {Boolean} fromMonday - false if weeks start from Sunday, true - from Monday.
 * @returns {number}
 */
const weeksInMonth = (year, month, fromMonday = false) => {
    const first = new Date(year, month, 1);
    const last  = new Date(year, month + 1, 0);
    let dayOfWeek = first.getDay();
    if (fromMonday && dayOfWeek === 0) dayOfWeek = 7;
    let days = dayOfWeek + last.getDate();
    if (fromMonday) days -= 1;
    return Math.ceil(days / 7);
}

---

You could use my time.js library. Here's the weeksInMonth function:

// http://github.com/augustl/time.js/blob/623e44e7a64fdaa3c908debdefaac1618a1ccde4/time.js#L67

weeksInMonth: function(){
  var millisecondsInThisMonth = this.clone().endOfMonth().epoch() - this.clone().firstDayInCalendarMonth().epoch();
  return Math.ceil(millisecondsInThisMonth / MILLISECONDS_IN_WEEK);
},

It might be a bit obscure since the meat of the functionality is in endOfMonth and firstDayInCalendarMonth, but you should at least be able to get some idea of how it works.

---

This works for me,

function(d){
    var firstDay = new Date(this.getFullYear(), this.getMonth(), 1).getDay();
    return Math.ceil((d.getDate() + (firstDay - 1))/7);
}

"d" should be the date.

---

A little rudimentary, yet should cater for original post :

/**
 * @param {date} 2020-01-30
 * @return {int} count
 */
this.numberOfCalendarWeekLines = date => {

    // get total
    let lastDayOfMonth = new Date( new Date( date ).getFullYear(), new Date( date ).getMonth() + 1, 0 );

    let manyDaysInMonth = lastDayOfMonth.getDate();

    // itterate through month - from 1st
    // count calender week lines by occurance
    // of a Saturday ( s m t w t f s )
    let countCalendarWeekLines = 0;

    for ( let i = 1; i <= manyDaysInMonth; i++ ) {

        if ( new Date( new Date( date ).setDate( i ) ).getDay() === 6 ) countCalendarWeekLines++;

    }

    // days after last occurance of Saturday 
    // leaked onto new line?
    if ( lastDayOfMonth.getDay() < 6 ) countCalendarWeekLines++;

    return countCalendarWeekLines;

};

---

Thanks to Ed Poor for his solution, this is the same as Date prototype.

Date.prototype.countWeeksOfMonth = function() {
  var year         = this.getFullYear();
  var month_number = this.getMonth();
  var firstOfMonth = new Date(year, month_number-1, 1);
  var lastOfMonth  = new Date(year, month_number, 0);
  var used         = firstOfMonth.getDay() + lastOfMonth.getDate();
  return Math.ceil( used / 7);
}

So you can use it like

var weeksInCurrentMonth = new Date().countWeeksOfMonth();
var weeksInDecember2012 = new Date(2012,12,1).countWeeksOfMonth(); // 6

---

function getWeeksInMonth(month_number, year) {
  console.log("year - "+year+" month - "+month_number+1);

  var day = 0;
  var firstOfMonth = new Date(year, month_number, 1);
  var lastOfMonth = new Date(year, parseInt(month_number)+1, 0);

  if (firstOfMonth.getDay() == 0) {
    day = 2;
    firstOfMonth = firstOfMonth.setDate(day);
    firstOfMonth = new Date(firstOfMonth);
  } else if (firstOfMonth.getDay() != 1) {
    day = 9-(firstOfMonth.getDay());
    firstOfMonth = firstOfMonth.setDate(day);
    firstOfMonth = new Date(firstOfMonth);
  }

  var days = (lastOfMonth.getDate() - firstOfMonth.getDate())+1
  return Math.ceil( days / 7);              
}

It worked for me. Please try

Thanks all

---

This piece of code give you the exact number of weeks in a given month:

Date.prototype.getMonthWeek = function(monthAdjustement)
{       
    var firstDay = new Date(this.getFullYear(), this.getMonth(), 1).getDay();
    var returnMessage = (Math.ceil(this.getDate()/7) + Math.floor(((7-firstDay)/7)));
    return returnMessage;
}

The monthAdjustement variable adds or substract the month that you are currently in

I use it in a calendar project in JS and the equivalent in Objective-C and it works well

---

    function weekCount(year, month_number, day_start) {

        // month_number is in the range 1..12
        // day_start is in the range 0..6 (where Sun=0, Mon=1, ... Sat=6)

        var firstOfMonth = new Date(year, month_number-1, 1);
        var lastOfMonth = new Date(year, month_number, 0);

        var dayOffset = (firstOfMonth.getDay() - day_start + 7) % 7;
        var used = dayOffset + lastOfMonth.getDate();

        return Math.ceil( used / 7);
    }

---

I know this is coming late, I have seen codes upon codes trying to get the number of weeks a particular month falls on, but many have not been really precise but most have been really informative and reusable, I'm not an expert programmer but I can really think and thanks to some codes by some people I was able to arrive at a conclusion.

function convertDate(date) {//i lost the guy who owns this code lol
var yyyy = date.getFullYear().toString();
var mm = (date.getMonth()+1).toString();
var dd  = date.getDate().toString();

var mmChars = mm.split('');
var ddChars = dd.split('');

return yyyy + '-' + (mmChars[1]?mm:"0"+mmChars[0]) + '-' + (ddChars[1]?dd:"0"+ddChars[0]);
}

//this line of code from https://stackoverflow.com/a/4028614/2540911
var days = ['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'];

var myDate = new Date('2019-03-2');  
//var myDate = new Date(); //or todays date

var c = convertDate(myDate).split("-"); 
let yr = c[0], mth = c[1], dy = c[2];

weekCount(yr, mth, dy)

//Ahh yes, this line of code is from Natim Up there, incredible work, https://stackoverflow.com/a/2485172/2540911
function weekCount(year, month_number, startDayOfWeek) {
// month_number is in the range 1..12
  console.log(weekNumber);

// Get the first day of week week day (0: Sunday, 1: Monday, ...)
var firstDayOfWeek = startDayOfWeek || 0;

var firstOfMonth = new Date(year, month_number-1, 1);
var lastOfMonth = new Date(year, month_number, 0);
var numberOfDaysInMonth = lastOfMonth.getDate();
var first = firstOfMonth.getDate();

//initialize first week
let weekNumber = 1;
while(first-1 < numberOfDaysInMonth){    
// add a day
firstOfMonth = firstOfMonth.setDate(firstOfMonth.getDate() + 1);//this line of code from https://stackoverflow.com/a/9989458/2540911
if(days[firstOfMonth.getDay()] === "Sunday"){//get new week every new sunday according the local date format
  //get newWeek
  weekNumber++;          
}

  if(weekNumber === 3 && days[firstOfMonth.getDay()] === "Friday")
    alert(firstOfMonth);

  first++
 }
}

I needed this code to generate a schedule or event scheduler for a church on every 3rd friday of a new month, so you can modify this to suit your or just pick your specific date, not "friday and specify the week of the month and Voila!! here you go

---

None of the solutions here really worked for me. Here is my crack at it.

// Example
// weeksOfMonth(2019, 9) // October
// Result: 5
weeksOfMonth (year, monthIndex) {
  const d = new Date(year, monthIndex+ 1, 0)
  const adjustedDate = d.getDate() + d.getDay()
  return Math.ceil(adjustedDate / 7)
}

---

Every solutions helped but nothing was working for me so I did my own with moment library :

const getWeeksInAMonth = (currentDate: string) => {
    const startOfMonth = moment(currentDate).startOf("month")
    const endOfMonth = moment(currentDate).endOf("month")
    return moment(endOfMonth).week() - moment(startOfMonth).week() + 1
}