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] 

}

It seems that moment.js does not have the method that implements the functionality that you are looking for. However, you can find the nth number of a certain day of the week in a month is using the Math.ceil of the date / 7 For example:

var firstFeb2014 = moment("2014-02-01"); //saturday
var day = firstFeb2014.day(); //6 = saturday
var nthOfMoth = Math.ceil(firstFeb2014.date() / 7); //1

var eightFeb2014 = moment("2014-02-08"); //saturday, the next one
console.log( Math.ceil(eightFeb2014.date() / 7) ); //prints 2, as expected

It looks like this is the number you are looking for, as demonstrated by the following test

function test(mJsDate){
   var str = mJsDate.toLocaleString().substring(0, 3) +
             " number " + Math.ceil(mJsDate.date() / 7) +
             " of the month";
   return str;
}

for(var i = 1; i <= 31; i++) {
   var dayStr = "2014-01-"+ i;
   console.log(dayStr + " " + test(moment(dayStr)) );
}

//examples from the console:
//2014-01-8 Wed number 2 of the month
//2014-01-13 Mon number 2 of the month
//2014-01-20 Mon number 3 of the month
//2014-01-27 Mon number 4 of the month
//2014-01-29 Wed number 5 of the month