Get Weeks In Month Through Javascript

Question

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 be able to know how many rows I need for a g

Answer 1

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))

Answer 2

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);
}

Answer 3

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

Answer 4

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

Answer 5

    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);
    }