Moment.js how to get week of month? (google calendar style)

When calculating the week of the month based on a given date, you have to take the offset into account. Not all months start on the first day of the week.

If you want to take this offset into account, you can use something something like the following if you are using moment.

function weekOfMonth (input = moment()) {
  const firstDayOfMonth = input.clone().startOf('month');
  const firstDayOfWeek = firstDayOfMonth.clone().startOf('week');

  const offset = firstDayOfMonth.diff(firstDayOfWeek, 'days');

  return Math.ceil((input.date() + offset) / 7);
}

Simple using moment.js

function week_of_month(date) {

        prefixes = [1,2,3,4,5];

    return prefixes[0 | moment(date).date() / 7] 

}

This library adds the function moment.weekMonth()
https://github.com/c-trimm/moment-recur

I made some modifications based on feedback.

let weeks = moment().weeks() - moment().startOf('month').weeks() + 1;
weeks = (weeks + 52) % 52;

On days passing through the next year, the week value will be negative so I had to add 52.

What about something like:

weekOfCurrentMonth = (moment().week() - (moment().month()*4));

This takes the current week of the year, and subtracts it by the 4 times the number of previous months. Which should give you the week of the current month

I think the answer to this question will be helpful, even though it doesn’t use moment.js as requested:

Get week of the month

function countWeekdayOccurrencesInMonth(date) {

    var m = moment(date),
            weekDay = m.day(),
            yearDay = m.dayOfYear(),
            count = 0;

    m.startOf('month');
    while (m.dayOfYear() <= yearDay) { 
        if (m.day() == weekDay) {
            count++; 
        }
        m.add('days', 1); 
    }

    return count;
}

There is a problem with @Daniel Earwicker answer.
I was using his function in my application and the while loop was infinite because of the following situation:

I was trying to figure out which week of december (2016) was the day 31.
the first day of december was day 336 of the year. The last day of december was day 366 of the year.

Problem here: When it was day 366 (31 of december, last day of the year) the code added another day to this date. But with another day added it would be day 1 of january of 2017. Therefore the loop never ended.

 while (m.dayOfYear() <= yearDay) { 

    if (m.day() == weekDay) {
        count++; 
    }
    m.add('days', 1); 
}

I added the following lines to the code so the problem would be fixed:

function countWeekdayOccurrencesInMonth(date) {

  var m = moment(date),
        weekDay = m.day(),
        yearDay = m.dayOfYear(),
        year = m.year(),
        count = 0;

 m.startOf('month');

 while (m.dayOfYear() <= yearDay && m.year() == year) {
    if (m.day() == weekDay) {
        count++;
    }
    m.add('days', 1);
 }

 return count;
}

It verifies if it is still in the same year of the date being veryfied

Here’s Robin Malfait‘s solution implemented with the lightweight library date-fns

import {
    differenceInDays,
    startOfMonth,
    startOfWeek,
    getDate
} from 'date-fns'

const weekOfMonth = function (date) {
    const firstDayOfMonth = startOfMonth(date)
    const firstDayOfWeek = startOfWeek(firstDayOfMonth)
    const offset = differenceInDays(firstDayOfMonth, firstDayOfWeek)
    return Math.ceil((getDate(date) + offset) / 7)
}

export default weekOfMonth

I’d do the following:

let todaysDate = moment(moment.now());
let endOfLastMonth = moment(get(this, 'todaysDate')).startOf('month').subtract(1, 'week');

let weekOfMonth = todaysDate.diff(endOfLastMonth, 'weeks');

That gets todaysDate and the endOfLastMonth and then uses Moment’s built-in diff() method to compute the current month’s week number.

It’s not built-in, but basically you can subtract the week number of the start of the month from the week number of the date in question.

function weekOfMonth(m) {
  return m.week() - moment(m).startOf('month').week() + 1;
}

Credit goes to code by original author, give him a star if it helped you.

How about this?

const moment = require("moment");

// Generate Week Number of The Month From Moment Date
function getWeekOfMonth(input = moment()) {
    let dayOfInput = input.clone().day(); // Saunday is 0 and Saturday is 6
    let diffToNextWeek = 7 - dayOfInput;
    let nextWeekStartDate = input.date() + diffToNextWeek;
    return Math.ceil((nextWeekStartDate) / 7);
}