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Add days but skip weekends

I have a small problem. I have a working code for adding days depending on the current time (if it is before 10am it adds 1 day if it is after 10am it adds 2 days for the date). So here is my question: How can I edit the code so it will skip the weekends in the calculations? For example, if I execute it before 10am on Friday it should show me the Monday date, not Saturday or Sunday.
function onGetMultiValue() {
var dzis = new Date();
var Godzina = new Date().getHours();
var teraz = dzis.getDate();
if (Godzina < 10) {
dzis.setDate(dzis.getDate() + 1);
} else {
dzis.setDate(dzis.getDate() + 2);
}
var day = dzis.getDate();
var month = dzis.getMonth() + 1;
var year = dzis.getFullYear();
var praca = day+"."+month+"."+year;
return praca;
}

You can use getDay() to check which day of the week it is.
function onGetMultiValue() {
const today = new Date();
const hour = new Date().getHours();
const dayOfWeek = today.getDay();
if (dayOfWeek == 5) {
// if it's Friday add 3 days to the date
today.setDate(today.getDate() + 3);
}
today.setDate(today.getDate() + hour < 10 ? 1 : 2)
const day = today.getDate();
const month = today.getMonth() + 1;
const year = today.getFullYear();
return `${day}.${month}.${year}`;
}
console.log(onGetMultiValue())

How to get a specify date in every month in Javascript?

I need to find this month, previous month and the next month of a specific date.
For example, date was set to 31 of every month, what I expect to get the date is
2018-02-28, 2018-03-31 and 2018-04-30. For those dates which has no 31, than it becomes the day before.
And finally generate 2 period, 2018-02-28 to 2018-03-29, 2018-03-30 to 2018-04-31.
I don't know how to handle feb and the month which less than 31.
var d = new Date();
var tyear = d.getFullYear(); //2018
var tmonth = d.getMonth(); //2
new Date(2018, tmonth-1, 31);//output 2018-03-02 not what I wanted

A simple algorithm is to add months to the original date, and if the new date is wrong, set it to the last day of the previous month. Keeping the original date values unmodified helps, e.g.
/* #param {Date} start - date to start
** #param {number} count - number of months to generate dates for
** #returns {Array} monthly Dates from start for count months
*/
function getMonthlyDates(start, count) {
var result = [];
var temp;
var year = start.getFullYear();
var month = start.getMonth();
var startDay = start.getDate();
for (var i=0; i<count; i++) {
temp = new Date(year, month + i, startDay);
if (temp.getDate() != startDay) temp.setDate(0);
result.push(temp);
}
return result;
}
// Start on 31 Jan in leap year
getMonthlyDates(new Date(2016,0,31), 4).forEach(d => console.log(d.toString()));
// Start on 31 Jan not in leap year
getMonthlyDates(new Date(2018,0,31), 4).forEach(d => console.log(d.toString()));
// Start on 30 Jan
getMonthlyDates(new Date(2018,0,30), 4).forEach(d => console.log(d.toString()));
// Start on 5 Jan
getMonthlyDates(new Date(2018,0,5), 4).forEach(d => console.log(d.toString()));

I think you're going to need an array with 12 numbers in it. Each number is the amount of days in each month and the numbers in the array go in order (first number is 31 because January has 31 days, second is 28 or 29 for Feb), etc. Then you'll get the month number from your input date and look in the array at the number corresponding to the month number +/- 1.
You'll then need to construct a date for the previous month and the next month based on the number of days in the current month.
See comments inline:
let daysInMonths = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
document.getElementById("date").addEventListener("input", function(){
console.clear();
// Create new Date based on value in date picker
var selectedDate = new Date(this.value + 'T00:00');
var year = selectedDate.getYear();
// Determine if it is a leap year (Feb has 29 days) and update array if so.
if (((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)) {
daysInMonths[1] = 29;
}
var selectedDateMonth = selectedDate.getMonth();
// Get previous month number (if current month is January, get December)
let prevMonth = selectedDateMonth > 0 ? selectedDateMonth - 1 : 11;
let prevMonthDate = null;
// If selected date is last day of month...
if(selectedDate.getDate() === daysInMonths[selectedDateMonth]){
// Create new date that takes the selected date and subtracts the correct amount of
// days from it based on a lookup in the array.
var newDate1 = new Date(selectedDate.getTime());
prevMonthDate =
new Date(newDate1.setDate(selectedDate.getDate() - daysInMonths[selectedDateMonth]));
} else {
// Create a new date that is last month and one day earlier
var newDate2 = new Date(selectedDate.getTime());
prevMonthDate =
new Date(new Date(newDate2.setDate(selectedDate.getDate() - 1))
.setMonth(selectedDate.getMonth() - 1));
}
// Get next month (if current month is December, get January
let nextMonth = selectedDateMonth < 11 ? selectedDateMonth + 1 : 0;
let nextMonthDate = null;
// Same idea for next month, but add instead of subtract.
// If selected date is last day of month...
if(selectedDate.getDate() === daysInMonths[selectedDateMonth]){
var newDate3 = new Date(selectedDate.getTime());
nextMonthDate =
new Date(newDate3.setDate(selectedDate.getDate() + daysInMonths[selectedDateMonth + 1]));
} else {
var newDate4 = new Date(selectedDate.getTime());
nextMonthDate = new Date(new Date(newDate4.setDate(selectedDate.getDate() + 1)).setMonth(selectedDate.getMonth() + 1));
}
console.log("Last month date: " + prevMonthDate.toLocaleDateString());
console.log("Next month date: " + nextMonthDate.toLocaleDateString());
});
<p>Pick a date: <input type="date" id="date"></p>

Use this approach:
Javascript Date Object – Adding and Subtracting Months
From the Author
There is a slight problem with the Javascript Date() Object when trying to advance to the next month or go back to the previous month.
For example, if your date is set to October 31, 2018 and you add one month, you'd probably expect the new date to be November 30, 2018 because November 31st doesn't exist. This, however, isn't the case.
Javascript automatically advances your Date object to December 1st. This functionality is very useful in most situations(i.e. adding days to a date, determining the number of days in a month or if it's a leap year), but not for adding/subtracting months. I've put together some functions below that extend the Date() object: nextMonth() and prevMonth().
function prevMonth() {
var thisMonth = this.getMonth();
this.setMonth(thisMonth - 1);
if (this.getMonth() != thisMonth - 1 && (this.getMonth() != 11 || (thisMonth == 11 && this.getDate() == 1)))
this.setDate(0);
}
function nextMonth() {
var thisMonth = this.getMonth();
this.setMonth(thisMonth + 1);
if (this.getMonth() != thisMonth + 1 && this.getMonth() != 0)
this.setDate(0);
}
Date.prototype.nextMonth = nextMonth;
Date.prototype.prevMonth = prevMonth;
var today = new Date(2018, 2, 31); //<----- March 31st, 2018
var prevMonth = new Date(today.getTime());
prevMonth.prevMonth();
console.log("Previous month:", prevMonth);
console.log("This month:", today)
var nextMonth = new Date(today.getTime());
nextMonth.nextMonth();
console.log("Next month:", nextMonth);
.as-console-wrapper { max-height: 100% !important; top: 0; }

Dates and time zones are a real pain in JS, so challenge accepted.
I broke it down in two steps:
- Count the days of prev and next month
- Compare with selected day and pick the lowest number
Testcases included
function createUTCDate(year, month, day) {
return new Date(Date.UTC(year, month, day));
}
function splitDate(date) {
return {
year: date.getUTCFullYear(),
month: date.getUTCMonth(),
day: date.getUTCDate()
};
}
function numberOfDaysInMonth(year, month) {
return new Date(year, month + 1, 0).getDate();
}
function dateNextMonth(dateObj) {
const daysNextMonth = numberOfDaysInMonth(dateObj.year, dateObj.month + 1);
const day = Math.min(daysNextMonth, dateObj.day);
return createUTCDate(dateObj.year, dateObj.month + 1, day);
}
function datePreviousMonth(dateObj) {
const daysPrevMonth = numberOfDaysInMonth(dateObj.year, dateObj.month - 1);
const day = Math.min(daysPrevMonth, dateObj.day);
return createUTCDate(dateObj.year, dateObj.month - 1, day);
}
const log = console.log;
function print(dateString) {
const date = new Date(dateString);
const dateObj = splitDate(date);
log("Previous: ", datePreviousMonth(dateObj).toISOString());
log("Selected: ", date.toISOString());
log("Next: ", dateNextMonth(dateObj).toISOString());
log("--------------");
}
const testCases = [
"2018-03-01 UTC",
"2018-03-31 UTC",
"2018-01-01 UTC",
"2018-12-31 UTC"
];
testCases.forEach(print);
Please note that the hack with new Date(xxx + " UTC") is not according to spec and is just there for testing purposes. Results may vary per browser.
You should choose an input format and construct your dates accordingly.

I handle it in a foolish way by concatenating string
let daysInMonths = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
let months = ["01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12"];
var target = nexttarget = lasttarget = "29"; //target day
if (((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)) {
daysInMonths[1] = 29;
}
function findLastDay(target, month){
if(target > daysInMonths[month]){
target = daysInMonths[month];
}
return target;
}
then
var d = new Date();
var year = d.getFullYear();
var month = d.getMonth();
target = findLastDay(target, month);
var this_month = year+"-"+months[month]+"-"+target;
console.log(this_month);//2018-03-29
// next month
if(month == 11){
nextmonth = 0;
nextyear = year + 1;
}else{
nextmonth = month+1;
nextyear = year;
}
nexttarget = findLastDay(nexttarget, nextmonth);
var next_month = nextyear+"-"+months[nextmonth]+"-"+nexttarget;
console.log(next_month);//2018-04-29
//last month
if(month == 0){
lastmonth = 11;
lastyear = year - 1;
}else{
lastmonth = month - 1;
lastyear = year;
}
lasttarget = findLastDay(lasttarget, lastmonth);
var last_month = lastyear+"-"+months[lastmonth]+"-"+lasttarget;
console.log(last_month);//2018-02-28

Date handling is tricky at the best of times. Don't do this yourself. Use Moment.js.
var target = 31;
var today = moment().date(target).calendar();
// today == '03/31/2018'
var nextMonth = moment().date(target).add(1, 'month').calendar();
// nextMonth == '04/30/2018'
var lastMonth = moment().date(target).subtract(1, 'month').calendar()
// lastMonth == '02/28/2018'

Is there a way that I can get the (first Sunday in October – first Sunday in April) with moment.js?

I know that I can use this for the start of the month moment().startOf('month') but I need the first Sunday of the month.

You could do this:
function getFirstWeekDay(dateString, dayOfWeek) {
var date = moment(dateString, "YYYY-MM-DD");
var day = date.day();
var diffDays = 0;
if (day > dayOfWeek) {
diffDays = 7 - (day - dayOfWeek);
} else {
diffDays = dayOfWeek - day
}
console.log(date.add(diffDays, 'day').format("YYYY-MM-DD"));
}
//Pass in the first of a given calendar month and the day weekday
getFirstWeekDay("2016-10-01", 0);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.15.1/moment.min.js"></script>

Please check this Code.
var d = new Date();
var first_week = d.getDate();
var the_day = d.getDay();
if(first_week <= 7 && the_day == 0)
{
// It's the first Sunday of the month
// Do more stuff here
}

Here is the sample using js to get the first sunday of any month or year
function firstSunday(month, year) {
let tempDate = new Date();
tempDate.setHours(0,0,0,0);
// first SUNDAY of april
tempDate.setMonth(month);
tempDate.setYear(year);
tempDate.setDate(1);
let day = tempDate.getDay();
let toNextSun = day !== 0 ? 7 - day : 0;
tempDate.setDate(tempDate.getDate() + toNextSun);
return tempDate.toDateString();
}
console.log("april first sunday" , firstSunday(3 , 2020));
console.log("oct first sunday" , firstSunday(9 , 2020))

Get next day, skip weekends

I want to generate next working day using JavaScript.
This is my code as of now
var today = new Date();
today.setDate(today.getDate());
var tdd = today.getDate();
var tmm = today.getMonth()+1;
var tyyyy = today.getYear();
var date = new Date();
date.setDate(date.getDate()+3);
Problem is, on Fridays it returns Saturday's date whereas I want it to be Monday

This will choose the next working day when a date is passed to it.
I suggest you normalise the date you pass, so you will not be surprised around summertime/wintertime change
Updated in 2023
const getNextWork = date => {
let day = date.getDay(), add = 1;
if (day === 6) add = 2; else
if (day === 5) add = 3;
date.setDate(date.getDate() + add); // will correctly handle 31+1 > 32 > 1st next month
return date;
};
// tests:
const dt = new Intl.DateTimeFormat("en-US", {
weekday: "short",
year: "numeric",
month: "long",
day: "numeric",
timeZone: "UTC",
timeZoneName: "short",
hour: "numeric",
minute: "numeric",
});
const aDay = 24 * 60 * 60 * 1000;
// 26th of March 2023 is daylight savings date in my country
let date = new Date(2023, 2, 24, 15, 0, 0, 0).getTime();
for (let i = 0; i < 7; i++) {
const d = new Date(date + i * aDay);
console.log(dt.format(d), "-->", dt.format(getNextWork(d)));
}
Older code:
var today = new Date(2016, 7, 26,12,0,0,0,0); // Friday at noon
console.log("today, Monday",today,"day #"+today.getDay());
var next = new Date(today.getTime());
next.setDate(next.getDate()+1); // tomorrow
while (next.getDay() == 6 || next.getDay() == 0) next.setDate(next.getDate() + 1);
console.log("no change ",next,"day #"+next.getDay());
console.log("-------");
// or without a loop:
function getNextWork(d) {
d.setDate(d.getDate()+1); // tomorrow
if (d.getDay()==0) d.setDate(d.getDate()+1);
else if (d.getDay()==6) d.setDate(d.getDate()+2);
return d;
}
next = getNextWork(today); // Friday
console.log("today, Friday",today);
console.log("next, Monday ",next);
console.log("-------");
today = new Date(2016, 7, 29,12,0,0,0); // Monday at noon
next = getNextWork(today); // Still Monday at noon
console.log("today, Monday",today);
console.log("no change ",next);
console.log("-------");
// Implementing Rob's comment
function getNextWork1(d) {
var day = d.getDay(),add=1;
if (day===5) add=3;
else if (day===6) add=2;
d.setDate(d.getDate()+add);
return d;
}
today = new Date(2016, 7, 26,12,0,0,0,0); // Friday at noon
next = getNextWork1(today); // Friday
console.log("today, Friday",today);
console.log("next, Monday ",next);
console.log("-------");
today = new Date(2016, 7, 26,12,0,0,0,0); // Monday at noon
next = getNextWork1(today); // Monday
console.log("today, Monday",today);
console.log("no change ",next);

You can add 1 day at at time until you get to a day that isn't Saturday or Sunday:
function getNextBusinessDay(date) {
// Copy date so don't affect original
date = new Date(+date);
// Add days until get not Sat or Sun
do {
date.setDate(date.getDate() + 1);
} while (!(date.getDay() % 6))
return date;
}
// today, Friday 26 Aug 2016
[new Date(), new Date(2016,7,26)].forEach(function(d) {
console.log(d.toLocaleString() + ' : ' + getNextBusinessDay(d).toLocaleString());
});
You can also test the day and add extra to get over the weekend:
// Classic Mon to Fri
function getNextWorkDay(date) {
let d = new Date(+date);
let day = d.getDay() || 7;
d.setDate(d.getDate() + (day > 4? 8 - day : 1));
return d;
}
for (let i=0, d=new Date(); i<7; i++) {
console.log(`${d.toDateString()} -> ${getNextWorkDay(d).toDateString()}`);
d.setDate(d.getDate() + 1);
}
Here is another approach where the work week can be specified using ECMAScript weekday numbers (Sun = 0, Mon = 1, etc.). Dates outside the range are shifted to the start of the next work week.
This is useful where the week is not the classic Mon to Fri, such as the Middle East where Sat to Wed is common or for some who might work Fri to Mon (or whatever).
function getNext(start, end, date) {
let d = new Date(+date);
d.setDate(d.getDate() + 1);
let day = d.getDay();
// Adjust end and day if necessary
// The order of tests and adjustment is important
if (end < start) {
if (day <= end) {
day += 7;
}
end += 7;
}
// If day is before start, shift to start
if (day < start) {
d.setDate(d.getDate() + start - day);
// If day is after end, shift to next start (treat Sunday as 7)
} else if (day > end) {
d.setDate(d.getDate() + 8 - (day || 7));
}
return d;
}
// Examples
let f = new Intl.DateTimeFormat('en-GB', {
weekday:'short',day:'2-digit', month:'short'});
let d = new Date();
[{c:'Work days Mon to Fri',s:1,e:5},
{c:'Work days Sat to Wed',s:6,e:3},
{c:'Work days Fri to Mon',s:5,e:1}
].forEach(({c,s,e}) => {
for (let i = 0; i < 7; i++) {
!i? console.log(`\n${c}`) : null;
console.log(`${f.format(d)} => ${f.format(getNext(s, e, d))}`);
d.setDate(d.getDate() + 1);
}
});

Check this out: https://jsfiddle.net/e9a4066r/
function get_next_weekday (date) {
var tomorrow = new Date(date.setDate(date.getDate() + 1))
return tomorrow.getDay() % 6
? tomorrow
: get_next_weekday(tomorrow)
}

The accepted answer will skip one day at a time, which answers the OPs question, but for anyone looking to add a variable number of days while still skipping weekends the function below may be helpful:
function addWorkDays(date, days) {
while (days > 0) {
date.setDate(date.getDate() + 1);
if (date.getDay() != 0 && date.getDay() != 6) {
days -= 1;
}
}
return date;
}

Thought I'd throw my hat in the ring here with:
function getNextBusinessDate(date) {
// Create date array [S, M, T, W, T, F, S]
const days = new Array(7);
let nextDate = date;
for(let i = 0; i < 7; i++) {
days[nextDate.getDay()] = new Date(nextDate);
nextDate.setDate(nextDate.getDate() + 1);
}
// Shift indices to index as though array was [M, T, W, T, F, S, S]
// Then truncate with min to make F, S, S all yield M for next date
return days[Math.min((date.getDay() + 6) % 7 + 1, 5) % 5 + 1];
}

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 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
}