Get a given weekday in a given month with JavaScript - javascript

I'm trying to get the nth weekday—for example, the second Sunday—of a month in which a certain date falls.
For instance, if the date is August 24, 2015, I'd like to do this:
nthDayOfMonth(0, 2, new Date(2015, 7, 24))
and get August 9, 2015 (2nd Sunday in August). I'd then like to be able to add a month to the date, call the function again, and get September 13, 2015 (2nd Sunday in September).
For some reason the below code is not working.
What am I missing?
function nthDayOfMonth(day, n, date) {
console.log(day);
console.log(n);
var count = 0;
var idate = new Date(date);
idate.setDate(1);
while ((count) < n) {
idate.setDate(idate.getDate() + 1);
if (idate.getDay() == day) {
count++;
}
}
return idate;
}


You have to check idate.getDay() before incrementing the day of the month. Otherwise you'll get an incorrect answer if the desired weekday falls on the first of the month.
The following snippet demonstrates the corrected function.
function print(s) {
document.write(s + '<br />');
}
function nthWeekdayOfMonth(weekday, n, date) {
var count = 0,
idate = new Date(date.getFullYear(), date.getMonth(), 1);
while (true) {
if (idate.getDay() === weekday) {
if (++count == n) {
break;
}
}
idate.setDate(idate.getDate() + 1);
}
return idate;
}
// Second Sunday of the current month.
var date = new Date();
print(date = nthWeekdayOfMonth(0, 2, date));
// Second Sunday of next month.
date.setMonth(date.getMonth() + 1);
print(date = nthWeekdayOfMonth(0, 2, date));
// First Tuesday of September 2015.
print(nthWeekdayOfMonth(2, 1, new Date(2015, 8)));
// First Wednesday of September 2015.
print(nthWeekdayOfMonth(3, 1, new Date(2015, 8)));
// Second Tuesday of September 2015.
print(nthWeekdayOfMonth(2, 2, new Date(2015, 8)));
// Second Wednesday of September 2015.
print(nthWeekdayOfMonth(3, 2, new Date(2015, 8)));
body {
font-family: sans-serif;
}
There's an even better approach that calculates the desired date without looping. We start by considering the weekday of the first day of the month. Suppose it's a Saturday, which JavaScript calls 6, and you're looking for a Sunday, which is 0.
To get to the first Sunday of the month, you have to advance the date by this number of days:
0 - 6 + 7
The result is 1. How does the calculation work? 0 - 6 is the number of days from weekday 6 to weekday 0, and to turn a negative value into a valid weekday, we add 7.
In general, the number of days from weekday a to weekday b is
(b - a + 7) % 7
To continue the example, suppose that we wanted the first Sunday of the month. In that case, we've arrived. But if we want the second day of the month, we have to advance the date by 7 more days. In general, given n such that n == 1 means the first occurrence of a given weekday, we have to advance by (n - 1) * 7 days.
To put it all together, if date is the first day of the month, we can get to the nth occurrence of weekday by advancing
(weekday - date.getDay() + 7) % 7 + (n - 1) * 7
days past the first day of the month.
This approach is implemented below.
function print(s) {
document.write(s + '<br />');
}
function nthWeekdayOfMonth(weekday, n, date) {
var date = new Date(date.getFullYear(), date.getMonth(), 1),
add = (weekday - date.getDay() + 7) % 7 + (n - 1) * 7;
date.setDate(1 + add);
return date;
}
// Second Sunday of the current month.
var date = new Date();
print(date = nthWeekdayOfMonth(0, 2, date));
// Second Sunday of next month.
date.setMonth(date.getMonth() + 1);
print(date = nthWeekdayOfMonth(0, 2, date));
// First Tuesday of September 2015.
print(nthWeekdayOfMonth(2, 1, new Date(2015, 8)));
// First Wednesday of September 2015.
print(nthWeekdayOfMonth(3, 1, new Date(2015, 8)));
// Second Tuesday of September 2015.
print(nthWeekdayOfMonth(2, 2, new Date(2015, 8)));
// Second Wednesday of September 2015.
print(nthWeekdayOfMonth(3, 2, new Date(2015, 8)));
body {
font-family: sans-serif;
}


Your code seems to work fine. To add a month, you can use d.setMonth(d.getMonth()+1).
Try this demo:
function nthDayOfMonth(day, n, date) {
var count = 0,
idate = new Date(date);
idate.setDate(1);
while (count < n) {
idate.setDate(idate.getDate() + 1);
if (idate.getDay() == day) { count++; }
}
return idate;
}
// Today : 2015-08-24
var today = new Date();
// Second Sunday of current month : 2015-08-09
var res = nthDayOfMonth(0, 2, today);
// res plus 1 month : 2015-09-09 (Wednesday)
var plusOne = new Date( res );
plusOne.setMonth(plusOne.getMonth() + 1);
// Second Sunday of next month : 2015-09-13
var res2 = nthDayOfMonth(0, 2, plusOne);
document.body.innerHTML = 'Today is <br>' + today + '<br>'
+ 'Second Sunday of current month is <br>' + res + '<br>'
+ 'If you add a month to it, you get <br>' + plusOne + '<br>'
+ 'And second Sunday of that month is <br>' + res2;


I just added a tweak to Michael Laszlo's excellent answer to allow the caller to provide n==5 (or any larger value) to indicate that the last weekday of the month is desired:
function nthWeekdayOfMonth(weekday, n, date) {
var month = date.getMonth();
var date = new Date(date.getFullYear(), month, 1),
add = (weekday - date.getDay() + 7) % 7 + (n - 1) * 7;
// make sure that we stay in the same month
do {
date.setMonth(month);
date.setDate(1 + add);
add -= 7;
} while (date.getMonth() != month);
return date;
}

Related

Date countown timer: minutes and seconds alwyas 59 with moment.js [duplicate]

How can one return the next date of a given weekday (it could be either a number 0-6 or names Sunday-Saturday).
Example, if today, on Friday 16-Oct-2009 I passed in:
Friday, it would return today's date 16-Oct-2009
Saturday returns 17-Oct-2009
Thursday returns 22-Oct-2009

Just adding 7 doesn't solve the problem.
The below function will give you the next day of the week.
function nextDay(x){
var now = new Date();
now.setDate(now.getDate() + (x+(7-now.getDay())) % 7);
return now;
}

Here's a slightly modified version to Tim's answer to address the specific question-- pass in a date d, and, and a desired day of week (dow 0-6), return the date
function nextDay(d, dow){
d.setDate(d.getDate() + (dow+(7-d.getDay())) % 7);
return d;
}

Here is another simple solution
//takes dayIndex from sunday(0) to saturday(6)
function nextDate(dayIndex) {
var today = new Date();
today.setDate(today.getDate() + (dayIndex - 1 - today.getDay() + 7) % 7 + 1);
return today;
}
document.write("Next Sunday is: "+nextDate(0).toLocaleString()+"<br/>");
document.write("Next Thursday is: "+nextDate(4).toLocaleString()+"<br/>");
document.write("Next Saturday is: "+nextDate(6).toLocaleString());

And if you do not want do pass numbers but weekday-names (sunday - saturday) to find a future date of a certain weekday, then this helps you as well:
function getDateOfWeekday(refday){
var days = {
monday: 1,
tuesday: 2,
wednesday: 3,
thursday: 4,
friday: 5,
saturday: 6,
sunday: 0
};
if(!days.hasOwnProperty(refday))throw new Error(refday+" is not listed in "+JSON.stringify(days));
var currDate = new Date();
var currTimestamp = currDate.getTime();
var triggerDay = days[refday];
var dayMillDiff=0;
var dayInMill = 1000*60*60*24;
// add a day to dayMillDiff as long as the desired refday (sunday for instance) is not reached
while(currDate.getDay()!=triggerDay){
dayMillDiff += dayInMill;
currDate = new Date(currDate.getTime()+dayInMill);
}
return new Date(currTimestamp + dayMillDiff);
}
var sunday = getDateOfWeekday("sunday");
document.write("Next Sunday is at: <strong>"+sunday.toLocaleString()+"</strong><br/>");
var thursday = getDateOfWeekday("thursday");
thursday.setHours(0,0,0,0); // set hours/minutes/seconds and millseconds to zero
document.write("Next Thursday is at: <strong>"+thursday.toLocaleString()+"</strong> on midnight<br/>");
var tuesday = getDateOfWeekday("tuesday");
document.write("Next Tuesday is at: <strong>"+tuesday.toLocaleString()+"</strong><br/>");

To expand on user 190106's answer, this code should give you what you wanted:
function getNextDay(day, resetTime){
var days = {
sunday: 0, monday: 1, tuesday: 2,
wednesday: 3, thursday: 4, friday: 5, saturday: 6
};
var dayIndex = days[day.toLowerCase()];
if (dayIndex !== undefined) {
throw new Error('"' + day + '" is not a valid input.');
}
var returnDate = new Date();
var returnDay = returnDate.getDay();
if (dayIndex !== returnDay) {
returnDate.setDate(returnDate.getDate() + (dayIndex + (7 - returnDay)) % 7);
}
if (resetTime) {
returnDate.setHours(0);
returnDate.setMinutes(0);
returnDate.setSeconds(0);
returnDate.setMilliseconds(0);
}
return returnDate;
}
alert(getNextDay('thursday', true));

A swiss-knife tool for javascript DateTime programming.
http://www.datejs.com/

Javascript Date for the Second Monday of the month

I am working with a group that meets the second monday of the month and they want their site to reflect the NEXT meeting date. I have the script to show this months second monday, but i am having trouble with the if else statement. I need it to reflect the next upcoming event and not just this months date. IE. this months event date was Aug 13 2012 which is past the current date (aug 21 2012). I would like it to move to the next available date Sept 10 2012. Below is the code i have so far.
<script type="text/javascript">
Date.prototype.x = function () {
var d = new Date (this.getFullYear(), this.getMonth(), 1, 0, 0, 0)
d.setDate (d.getDate() + 15 - d.getDay())
return d
}
Date.prototype.getSecondMonday = function () {
var d = new Date (this.getFullYear(), 1, 1, 0, 0, 0)
d.setMonth(this.getMonth()+1)
d.setDate (d.getDate() + 15 - d.getDay())
return d
}
var today = new Date()
var todayDate = today.toDateString()
if (Date.prototype.x>todayDate)
{
document.write (new Date().x().toDateString());
}
else
{
document.write (new Date().getSecondMonday().toDateString());
}
</script>

If the date of the second Monday of the current month is less than the current date,
call the function on the first of the next month.
Date.prototype.nextSecondMonday= function(){
var temp= new Date(this), d= temp.getDate(), n= 1;
while(temp.getDay()!= 1) temp.setDate(++n);
temp.setDate(n+7);
if(d>temp.getDate()){
temp.setMonth(temp.getMonth()+1, 1);
return temp.nextSecondMonday();
}
return temp.toLocaleDateString();
}
/* tests
var x= new Date(2012, 7, 22);
x.nextSecondMonday()
Monday, September 10, 2012
var x= new Date(2012, 7, 12);
x.nextSecondMonday()
Monday, August 13, 2012
*/

You're missing () for the x function, so it's not executing it. :) Should be:
if (Date.prototype.x() > todayDate)
UPDATE:
Here is a fixed/working version of the logic cleaned up (and probably overly commented, but I guess it's at least there if anyone needs it).
Date.prototype.nextSecondMonday = function (){
// Load the month.
var target = new Date(this.getFullYear(), this.getMonth(), 1, 0, 0, 0);
var today = new Date();
// Check to see if the 1st is on a Monday.
var isMonday = (target.getDay() == 1);
// Jump ahead two weeks from the 1st, and move back the appropriate number of days to reach the preceding Monday.
// i.e. If the 1st is a Thursday, we would move back three days.
var targetDate = 15 - (target.getDay() - 1);
// Quick adjustment if the 1st is a Monday.
if (isMonday) targetDate -= 7;
// Move to the second Monday in the month.
target.setDate(targetDate);
// Second Monday is before today's date, so find the second Monday next month.
if (today > target) {
//return "<em>" + target.toLocaleDateString() + " is in the past...</em>";
target.setMonth(target.getMonth() + 1);
return target.nextSecondMonday();
}
// Format and return string date of second Monday.
return target.toLocaleDateString();
}
// Working test for the year 2012.
//for (var i = 0; i < 12; i++)
//$("#log").append(new Date(2012, i).nextSecondMonday() + "<br /><br />");

How to convert a week number to a date in Javascript

I had tried to find some work done but I haven't had luck. Any ideas?
Examples:
Week, 1, 2001 => 2001-01-01
Week, 26, 2007 => 2007-06-01

As Kevin's code does not implement ISO 8601 properly (first day of the first week of year must be a Monday), I've corrected it and ended up with (also check it on jsfiddle):
function firstDayOfWeek(week, year) {
if (year==null) {
year = (new Date()).getFullYear();
}
var date = firstWeekOfYear(year),
weekTime = weeksToMilliseconds(week),
targetTime = date.getTime() + weekTime;
return date.setTime(targetTime);
}
function weeksToMilliseconds(weeks) {
return 1000 * 60 * 60 * 24 * 7 * (weeks - 1);
}
function firstWeekOfYear(year) {
var date = new Date();
date = firstDayOfYear(date,year);
date = firstWeekday(date);
return date;
}
function firstDayOfYear(date, year) {
date.setYear(year);
date.setDate(1);
date.setMonth(0);
date.setHours(0);
date.setMinutes(0);
date.setSeconds(0);
date.setMilliseconds(0);
return date;
}
/**
* Sets the given date as the first day of week of the first week of year.
*/
function firstWeekday(firstOfJanuaryDate) {
// 0 correspond au dimanche et 6 correspond au samedi.
var FIRST_DAY_OF_WEEK = 1; // Monday, according to iso8601
var WEEK_LENGTH = 7; // 7 days per week
var day = firstOfJanuaryDate.getDay();
day = (day === 0) ? 7 : day; // make the days monday-sunday equals to 1-7 instead of 0-6
var dayOffset=-day+FIRST_DAY_OF_WEEK; // dayOffset will correct the date in order to get a Monday
if (WEEK_LENGTH-day+1<4) {
// the current week has not the minimum 4 days required by iso 8601 => add one week
dayOffset += WEEK_LENGTH;
}
return new Date(firstOfJanuaryDate.getTime()+dayOffset*24*60*60*1000);
}
function assertDateEquals(effectiveDate, expectedDate, description) {
if ((effectiveDate==null ^ expectedDate==null) || effectiveDate.getTime()!=expectedDate.getTime()) {
console.log("assert failed: "+description+"; effective="+effectiveDate+", expected="+expectedDate);
}
}
function assertEquals(effectiveValue, expectedValue, description) {
if (effectiveValue!=expectedValue) {
console.log("assert failed: "+description+"; effective="+effectiveValue+", expected="+expectedValue);
}
}
// expect the first day of year to be a monday
for (var i=1970; i<2050; i++) {
assertEquals(firstWeekOfYear(i).getDay(), 1, "first day of year "+i+" must be a monday"); // 1=Monday
}
// assert some future first day of first week of year; source: http://www.epochconverter.com/date-and-time/weeknumbers-by-year.php
assertDateEquals(firstWeekOfYear(2013), new Date(Date.parse("Dec 31, 2012")), "2013");
assertDateEquals(firstWeekOfYear(2014), new Date(Date.parse("Dec 30, 2013")), "2014");
assertDateEquals(firstWeekOfYear(2015), new Date(Date.parse("Dec 29, 2014")), "2015");
assertDateEquals(firstWeekOfYear(2016), new Date(Date.parse("Jan 4, 2016")), "2016");
assertDateEquals(firstWeekOfYear(2017), new Date(Date.parse("Jan 2, 2017")), "2017");
assertDateEquals(firstWeekOfYear(2018), new Date(Date.parse("Jan 1, 2018")), "2018");
assertDateEquals(firstWeekOfYear(2019), new Date(Date.parse("Dec 31, 2018")), "2019");
assertDateEquals(firstWeekOfYear(2020), new Date(Date.parse("Dec 30, 2019")), "2020");
assertDateEquals(firstWeekOfYear(2021), new Date(Date.parse("Jan 4, 2021")), "2021");
assertDateEquals(firstWeekOfYear(2022), new Date(Date.parse("Jan 3, 2022")), "2022");
assertDateEquals(firstWeekOfYear(2023), new Date(Date.parse("Jan 2, 2023")), "2023");
assertDateEquals(firstWeekOfYear(2024), new Date(Date.parse("Jan 1, 2024")), "2024");
assertDateEquals(firstWeekOfYear(2025), new Date(Date.parse("Dec 30, 2024")), "2025");
assertDateEquals(firstWeekOfYear(2026), new Date(Date.parse("Dec 29, 2025")), "2026");
console.log("All assertions done.");
I included test cases for some dates to check that the first day of the first week of year is a Monday and checked some dates based on http://www.epochconverter.com/date-and-time/weeknumbers-by-year.php

Someone might be still interested in a more contained version:
function firstDayOfWeek (year, week) {
// Jan 1 of 'year'
var d = new Date(year, 0, 1),
offset = d.getTimezoneOffset();
// ISO: week 1 is the one with the year's first Thursday
// so nearest Thursday: current date + 4 - current day number
// Sunday is converted from 0 to 7
d.setDate(d.getDate() + 4 - (d.getDay() || 7));
// 7 days * (week - overlapping first week)
d.setTime(d.getTime() + 7 * 24 * 60 * 60 * 1000
* (week + (year == d.getFullYear() ? -1 : 0 )));
// daylight savings fix
d.setTime(d.getTime()
+ (d.getTimezoneOffset() - offset) * 60 * 1000);
// back to Monday (from Thursday)
d.setDate(d.getDate() - 3);
return d;
}

I took the original idea from Kevin, with some tweaks, coz the original code is returning milliseconds. Here you go:
var d = firstDayOfWeek(9, 2013);
console.log(d.format("yyyy-MM-dd"));
////////////////////////////// Main Code //////////////////////////////
function firstDayOfWeek(week, year) {
if (typeof year !== 'undefined') {
year = (new Date()).getFullYear();
}
var date = firstWeekOfYear(year),
weekTime = weeksToMilliseconds(week),
targetTime = date.getTime() + weekTime - 86400000;
var result = new Date(targetTime)
return result;
}
function weeksToMilliseconds(weeks) {
return 1000 * 60 * 60 * 24 * 7 * (weeks - 1);
}
function firstWeekOfYear(year) {
var date = new Date();
date = firstDayOfYear(date,year);
date = firstWeekday(date);
return date;
}
function firstDayOfYear(date, year) {
date.setYear(year);
date.setDate(1);
date.setMonth(0);
date.setHours(0);
date.setMinutes(0);
date.setSeconds(0);
date.setMilliseconds(0);
return date;
}
function firstWeekday(date) {
var day = date.getDay(),
day = (day === 0) ? 7 : day;
if (day > 3) {
var remaining = 8 - day,
target = remaining + 1;
date.setDate(target);
}
return date;
}

Take a look at this fiddle. First, it gets the first week of the specified year. This takes into account that according to ISO 8601 the first week of the year is the first week containing a wednesday. Then it adds the weeks to the acquired date and returns the result.
function firstDayOfWeek(week, year) {
var date = firstWeekOfYear(year),
weekTime = weeksToMilliseconds(week),
targetTime = weekTime + date.getTime();
return date.setTime(targetTime);
}

Get week of year in JavaScript like in PHP

How do I get the current weeknumber of the year, like PHP's date('W')?
It should be the ISO-8601 week number of year, weeks starting on Monday.

You should be able to get what you want here: http://www.merlyn.demon.co.uk/js-date6.htm#YWD.
A better link on the same site is: Working with weeks.
Edit
Here is some code based on the links provided and that posted eariler by Dommer. It has been lightly tested against results at http://www.merlyn.demon.co.uk/js-date6.htm#YWD. Please test thoroughly, no guarantee provided.
Edit 2017
There was an issue with dates during the period that daylight saving was observed and years where 1 Jan was Friday. Fixed by using all UTC methods. The following returns identical results to Moment.js.
/* For a given date, get the ISO week number
*
* Based on information at:
*
* THIS PAGE (DOMAIN EVEN) DOESN'T EXIST ANYMORE UNFORTUNATELY
* http://www.merlyn.demon.co.uk/weekcalc.htm#WNR
*
* Algorithm is to find nearest thursday, it's year
* is the year of the week number. Then get weeks
* between that date and the first day of that year.
*
* Note that dates in one year can be weeks of previous
* or next year, overlap is up to 3 days.
*
* e.g. 2014/12/29 is Monday in week 1 of 2015
* 2012/1/1 is Sunday in week 52 of 2011
*/
function getWeekNumber(d) {
// Copy date so don't modify original
d = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
// Set to nearest Thursday: current date + 4 - current day number
// Make Sunday's day number 7
d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay()||7));
// Get first day of year
var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1));
// Calculate full weeks to nearest Thursday
var weekNo = Math.ceil(( ( (d - yearStart) / 86400000) + 1)/7);
// Return array of year and week number
return [d.getUTCFullYear(), weekNo];
}
var result = getWeekNumber(new Date());
document.write('It\'s currently week ' + result[1] + ' of ' + result[0]);
Hours are zeroed when creating the "UTC" date.
Minimized, prototype version (returns only week-number):
Date.prototype.getWeekNumber = function(){
var d = new Date(Date.UTC(this.getFullYear(), this.getMonth(), this.getDate()));
var dayNum = d.getUTCDay() || 7;
d.setUTCDate(d.getUTCDate() + 4 - dayNum);
var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1));
return Math.ceil((((d - yearStart) / 86400000) + 1)/7)
};
document.write('The current ISO week number is ' + new Date().getWeekNumber());
Test section
In this section, you can enter any date in YYYY-MM-DD format and check that this code gives the same week number as Moment.js ISO week number (tested over 50 years from 2000 to 2050).
Date.prototype.getWeekNumber = function(){
var d = new Date(Date.UTC(this.getFullYear(), this.getMonth(), this.getDate()));
var dayNum = d.getUTCDay() || 7;
d.setUTCDate(d.getUTCDate() + 4 - dayNum);
var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1));
return Math.ceil((((d - yearStart) / 86400000) + 1)/7)
};
function checkWeek() {
var s = document.getElementById('dString').value;
var m = moment(s, 'YYYY-MM-DD');
document.getElementById('momentWeek').value = m.format('W');
document.getElementById('answerWeek').value = m.toDate().getWeekNumber();
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
Enter date YYYY-MM-DD: <input id="dString" value="2021-02-22">
<button onclick="checkWeek(this)">Check week number</button><br>
Moment: <input id="momentWeek" readonly><br>
Answer: <input id="answerWeek" readonly>

You can use momentjs library also:
moment().format('W')

Not ISO-8601 week number but if the search engine pointed you here anyway.
As said above but without a class:
let now = new Date();
let onejan = new Date(now.getFullYear(), 0, 1);
let week = Math.ceil((((now.getTime() - onejan.getTime()) / 86400000) + onejan.getDay() + 1) / 7);
console.log(week);

Accordily http://javascript.about.com/library/blweekyear.htm
Date.prototype.getWeek = function() {
var onejan = new Date(this.getFullYear(), 0, 1);
var millisecsInDay = 86400000;
return Math.ceil((((this - onejan) / millisecsInDay) + onejan.getDay() + 1) / 7);
};
let d = new Date(2020,11,30);
for (let i=0; i<14; i++) {
console.log(`${d.toDateString()} is week ${d.getWeek()}`);
d.setDate(d.getDate() + 1);
}

Jacob Wright's Date.format() library implements date formatting in the style of PHP's date() function and supports the ISO-8601 week number:
new Date().format('W');
It may be a bit overkill for just a week number, but it does support PHP style formatting and is quite handy if you'll be doing a lot of this.

The code below calculates the correct ISO 8601 week number. It matches PHP's date("W") for every week between 1/1/1970 and 1/1/2100.
/**
* Get the ISO week date week number
*/
Date.prototype.getWeek = function () {
// Create a copy of this date object
var target = new Date(this.valueOf());
// ISO week date weeks start on Monday, so correct the day number
var dayNr = (this.getDay() + 6) % 7;
// ISO 8601 states that week 1 is the week with the first Thursday of that year
// Set the target date to the Thursday in the target week
target.setDate(target.getDate() - dayNr + 3);
// Store the millisecond value of the target date
var firstThursday = target.valueOf();
// Set the target to the first Thursday of the year
// First, set the target to January 1st
target.setMonth(0, 1);
// Not a Thursday? Correct the date to the next Thursday
if (target.getDay() !== 4) {
target.setMonth(0, 1 + ((4 - target.getDay()) + 7) % 7);
}
// The week number is the number of weeks between the first Thursday of the year
// and the Thursday in the target week (604800000 = 7 * 24 * 3600 * 1000)
return 1 + Math.ceil((firstThursday - target) / 604800000);
}
Source: Taco van den Broek
If you're not into extending prototypes, then here's a function:
function getWeek(date) {
if (!(date instanceof Date)) date = new Date();
// ISO week date weeks start on Monday, so correct the day number
var nDay = (date.getDay() + 6) % 7;
// ISO 8601 states that week 1 is the week with the first Thursday of that year
// Set the target date to the Thursday in the target week
date.setDate(date.getDate() - nDay + 3);
// Store the millisecond value of the target date
var n1stThursday = date.valueOf();
// Set the target to the first Thursday of the year
// First, set the target to January 1st
date.setMonth(0, 1);
// Not a Thursday? Correct the date to the next Thursday
if (date.getDay() !== 4) {
date.setMonth(0, 1 + ((4 - date.getDay()) + 7) % 7);
}
// The week number is the number of weeks between the first Thursday of the year
// and the Thursday in the target week (604800000 = 7 * 24 * 3600 * 1000)
return 1 + Math.ceil((n1stThursday - date) / 604800000);
}
Sample usage:
getWeek(); // Returns 37 (or whatever the current week is)
getWeek(new Date('Jan 2, 2011')); // Returns 52
getWeek(new Date('Jan 1, 2016')); // Returns 53
getWeek(new Date('Jan 4, 2016')); // Returns 1

getWeekOfYear: function(date) {
var target = new Date(date.valueOf()),
dayNumber = (date.getUTCDay() + 6) % 7,
firstThursday;
target.setUTCDate(target.getUTCDate() - dayNumber + 3);
firstThursday = target.valueOf();
target.setUTCMonth(0, 1);
if (target.getUTCDay() !== 4) {
target.setUTCMonth(0, 1 + ((4 - target.getUTCDay()) + 7) % 7);
}
return Math.ceil((firstThursday - target) / (7 * 24 * 3600 * 1000)) + 1;
}
Following code is timezone-independent (UTC dates used) and works according to the https://en.wikipedia.org/wiki/ISO_8601

Get the weeknumber of any given Date
function week(year,month,day) {
function serial(days) { return 86400000*days; }
function dateserial(year,month,day) { return (new Date(year,month-1,day).valueOf()); }
function weekday(date) { return (new Date(date)).getDay()+1; }
function yearserial(date) { return (new Date(date)).getFullYear(); }
var date = year instanceof Date ? year.valueOf() : typeof year === "string" ? new Date(year).valueOf() : dateserial(year,month,day),
date2 = dateserial(yearserial(date - serial(weekday(date-serial(1))) + serial(4)),1,3);
return ~~((date - date2 + serial(weekday(date2) + 5))/ serial(7));
}
Example
console.log(
week(2016, 06, 11),//23
week(2015, 9, 26),//39
week(2016, 1, 1),//53
week(2016, 1, 4),//1
week(new Date(2016, 0, 4)),//1
week("11 january 2016")//2
);

I found useful the Java SE's SimpleDateFormat class described on Oracle's specification:
http://goo.gl/7MbCh5. In my case in Google Apps Script it worked like this:
function getWeekNumber() {
var weekNum = parseInt(Utilities.formatDate(new Date(), "GMT", "w"));
Logger.log(weekNum);
}
For example in a spreadsheet macro you can retrieve the actual timezone of the file:
function getWeekNumber() {
var weekNum = parseInt(Utilities.formatDate(new Date(), SpreadsheetApp.getActiveSpreadsheet().getSpreadsheetTimeZone(), "w"));
Logger.log(weekNum);
}

This adds "getWeek" method to Date.prototype which returns number of week from the beginning of the year. The argument defines which day of the week to consider the first. If no argument passed, first day is assumed Sunday.
/**
* Get week number in the year.
* #param {Integer} [weekStart=0] First day of the week. 0-based. 0 for Sunday, 6 for Saturday.
* #return {Integer} 0-based number of week.
*/
Date.prototype.getWeek = function(weekStart) {
var januaryFirst = new Date(this.getFullYear(), 0, 1);
if(weekStart !== undefined && (typeof weekStart !== 'number' || weekStart % 1 !== 0 || weekStart < 0 || weekStart > 6)) {
throw new Error('Wrong argument. Must be an integer between 0 and 6.');
}
weekStart = weekStart || 0;
return Math.floor((((this - januaryFirst) / 86400000) + januaryFirst.getDay() - weekStart) / 7);
};

If you are already in an Angular project you could use $filter('date').
For example:
var myDate = new Date();
var myWeek = $filter('date')(myDate, 'ww');

The code snippet which works pretty well for me is this one:
var yearStart = +new Date(d.getFullYear(), 0, 1);
var today = +new Date(d.getFullYear(),d.getMonth(),d.getDate());
var dayOfYear = ((today - yearStart + 1) / 86400000);
return Math.ceil(dayOfYear / 7).toString();
Note:
d is my Date for which I want the current week number.
The + converts the Dates into numbers (working with TypeScript).

With Luxon (https://github.com/moment/luxon) :
import { DateTime } from 'luxon';
const week: number = DateTime.fromJSDate(new Date()).weekNumber;

This week number thing has been a real pain in the a**. Most trivial solutions around the web didn't really work for me as they worked most of the time but all of them broke at some point, especially when year changed and last week of the year was suddenly next year's first week etc. Even Angular's date filter showed incorrect data (it was the 1st week of next year, Angular gave week 53).
Note: The examples are designed to work with European weeks (Mon first)!
getWeek()
Date.prototype.getWeek = function(){
// current week's Thursday
var curWeek = new Date(this.getTime());
curWeek.setDay(4);
// current year's first week's Thursday
var firstWeek = new Date(curWeek.getFullYear(), 0, 4);
firstWeek.setDay(4);
return (curWeek.getDayIndex() - firstWeek.getDayIndex()) / 7 + 1;
};
setDay()
/**
* Make a setDay() prototype for Date
* Sets week day for the date
*/
Date.prototype.setDay = function(day){
// Get day and make Sunday to 7
var weekDay = this.getDay() || 7;
var distance = day - weekDay;
this.setDate(this.getDate() + distance);
return this;
}
getDayIndex()
/*
* Returns index of given date (from Jan 1st)
*/
Date.prototype.getDayIndex = function(){
var start = new Date(this.getFullYear(), 0, 0);
var diff = this - start;
var oneDay = 86400000;
return Math.floor(diff / oneDay);
};
I have tested this and it seems to be working very well but if you notice a flaw in it, please let me know.

Here is my implementation for calculating the week number in JavaScript. corrected for summer and winter time offsets as well.
I used the definition of the week from this article: ISO 8601
Weeks are from mondays to sunday, and january 4th is always in the first week of the year.
// add get week prototype functions
// weeks always start from monday to sunday
// january 4th is always in the first week of the year
Date.prototype.getWeek = function () {
year = this.getFullYear();
var currentDotw = this.getWeekDay();
if (this.getMonth() == 11 && this.getDate() - currentDotw > 28) {
// if true, the week is part of next year
return this.getWeekForYear(year + 1);
}
if (this.getMonth() == 0 && this.getDate() + 6 - currentDotw < 4) {
// if true, the week is part of previous year
return this.getWeekForYear(year - 1);
}
return this.getWeekForYear(year);
}
// returns a zero based day, where monday = 0
// all weeks start with monday
Date.prototype.getWeekDay = function () {
return (this.getDay() + 6) % 7;
}
// corrected for summer/winter time
Date.prototype.getWeekForYear = function (year) {
var currentDotw = this.getWeekDay();
var fourjan = new Date(year, 0, 4);
var firstDotw = fourjan.getWeekDay();
var dayTotal = this.getDaysDifferenceCorrected(fourjan) // the difference in days between the two dates.
// correct for the days of the week
dayTotal += firstDotw; // the difference between the current date and the first monday of the first week,
dayTotal -= currentDotw; // the difference between the first monday and the current week's monday
// day total should be a multiple of 7 now
var weeknumber = dayTotal / 7 + 1; // add one since it gives a zero based week number.
return weeknumber;
}
// corrected for timezones and offset
Date.prototype.getDaysDifferenceCorrected = function (other) {
var millisecondsDifference = (this - other);
// correct for offset difference. offsets are in minutes, the difference is in milliseconds
millisecondsDifference += (other.getTimezoneOffset()- this.getTimezoneOffset()) * 60000;
// return day total. 1 day is 86400000 milliseconds, floor the value to return only full days
return Math.floor(millisecondsDifference / 86400000);
}
for testing i used the following JavaScript tests in Qunit
var runweekcompare = function(result, expected) {
equal(result, expected,'Week nr expected value: ' + expected + ' Actual value: ' + result);
}
test('first week number test', function () {
expect(5);
var temp = new Date(2016, 0, 4); // is the monday of the first week of the year
runweekcompare(temp.getWeek(), 1);
var temp = new Date(2016, 0, 4, 23, 50); // is the monday of the first week of the year
runweekcompare(temp.getWeek(), 1);
var temp = new Date(2016, 0, 10, 23, 50); // is the sunday of the first week of the year
runweekcompare(temp.getWeek(), 1);
var temp = new Date(2016, 0, 11, 23, 50); // is the second week of the year
runweekcompare(temp.getWeek(), 2);
var temp = new Date(2016, 1, 29, 23, 50); // is the 9th week of the year
runweekcompare(temp.getWeek(), 9);
});
test('first day is part of last years last week', function () {
expect(2);
var temp = new Date(2016, 0, 1, 23, 50); // is the first last week of the previous year
runweekcompare(temp.getWeek(), 53);
var temp = new Date(2011, 0, 2, 23, 50); // is the first last week of the previous year
runweekcompare(temp.getWeek(), 52);
});
test('last day is part of next years first week', function () {
var temp = new Date(2013, 11, 30); // is part of the first week of 2014
runweekcompare(temp.getWeek(), 1);
});
test('summer winter time change', function () {
expect(2);
var temp = new Date(2000, 2, 26);
runweekcompare(temp.getWeek(), 12);
var temp = new Date(2000, 2, 27);
runweekcompare(temp.getWeek(), 13);
});
test('full 20 year test', function () {
//expect(20 * 12 * 28 * 2);
for (i = 2000; i < 2020; i++) {
for (month = 0; month < 12; month++) {
for (day = 1; day < 29 ; day++) {
var temp = new Date(i, month, day);
var expectedweek = temp.getWeek();
var temp2 = new Date(i, month, day, 23, 50);
var resultweek = temp.getWeek();
equal(expectedweek, Math.round(expectedweek), 'week number whole number expected ' + Math.round(expectedweek) + ' resulted week nr ' + expectedweek);
equal(resultweek, expectedweek, 'Week nr expected value: ' + expectedweek + ' Actual value: ' + resultweek + ' for year ' + i + ' month ' + month + ' day ' + day);
}
}
}
});

Here is a slight adaptation for Typescript that will also return the dates for the week start and week end. I think it's common to have to display those in a user interface, since people don't usually remember week numbers.
function getWeekNumber(d: Date) {
// Copy date so don't modify original
d = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
// Set to nearest Thursday: current date + 4 - current day number Make
// Sunday's day number 7
d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay() || 7));
// Get first day of year
const yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
// Calculate full weeks to nearest Thursday
const weekNo = Math.ceil(
((d.getTime() - yearStart.getTime()) / 86400000 + 1) / 7
);
const weekStartDate = new Date(d.getTime());
weekStartDate.setUTCDate(weekStartDate.getUTCDate() - 3);
const weekEndDate = new Date(d.getTime());
weekEndDate.setUTCDate(weekEndDate.getUTCDate() + 3);
return [d.getUTCFullYear(), weekNo, weekStartDate, weekEndDate] as const;
}

This is my typescript implementation which I tested against some dates. This implementation allows you to set the first day of the week to any day.
//sunday = 0, monday = 1, ...
static getWeekNumber(date: Date, firstDay = 1): number {
const d = new Date(date.getTime());
d.setHours(0, 0, 0, 0);
//Set to first day of the week since it is the same weeknumber
while(d.getDay() != firstDay){
d.setDate(d.getDate() - 1);
}
const dayOfYear = this.getDayOfYear(d);
let weken = Math.floor(dayOfYear/7);
// add an extra week if 4 or more days are in this year.
const daysBefore = ((dayOfYear % 7) - 1);
if(daysBefore >= 4){
weken += 1;
}
//if the last 3 days onf the year,it is the first week
const t = new Date(d.getTime());
t.setDate(t.getDate() + 3);
if(t.getFullYear() > d.getFullYear()){
return 1;
}
weken += 1;
return weken;
}
private static getDayOfYear(date: Date){
const start = new Date(date.getFullYear(), 0, 0);
const diff = (date.getTime() - start.getTime()) + ((start.getTimezoneOffset() - date.getTimezoneOffset()) * 60 * 1000);
const oneDay = 1000 * 60 * 60 * 24;
const day = Math.floor(diff / oneDay);
return day;
}
Tests:
describe('getWeeknumber', () => {
it('should be ok for 0 sunday', () => {
expect(DateUtils.getWeekNumber(new Date(2015, 0, 4), 0)).toBe(1);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 1), 0)).toBe(1);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 2), 0)).toBe(1);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 8), 0)).toBe(2);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 9), 0)).toBe(2);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 28), 0)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 29), 0)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 30), 0)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 31), 0)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2022, 0, 3), 0)).toBe(1);
});
it('should be ok for monday 1 default', () => {
expect(DateUtils.getWeekNumber(new Date(2015, 0, 4), 1)).toBe(1);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 1), 1)).toBe(52);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 2), 1)).toBe(1);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 8), 1)).toBe(1);
expect(DateUtils.getWeekNumber(new Date(2017, 0, 9), 1)).toBe(2);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 28), 1)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 29), 1)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 30), 1)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2020, 11, 31), 1)).toBe(53);
expect(DateUtils.getWeekNumber(new Date(2022, 0, 3), 1)).toBe(1);
});
});

I tried a lot to get the shortest code to get the weeknumber ISO-conform.
Date.prototype.getWeek=function(){
var date=new Date(this);
date.setHours(0,0,0,0);
return Math.round(((date.setDate(this.getDate()+2-(this.getDay()||7))-date.setMonth(0,4))/8.64e7+3+(date.getDay()||7))/7)+"/"+date.getFullYear();}
The variable date is necessary to avoid to alter the original this. I used the return values of setDate() and setMonth() to dispense with getTime() to save code length and I used an expontial number for milliseconds of a day instead of a multiplication of single elements or a number with five zeros. this is Date or Number of milliseconds, return value is String e.g. "49/2017".

Another library-based option: use d3-time-format:
const formatter = d3.timeFormat('%U');
const weekNum = formatter(new Date());

Shortest workaround for Angular2+ DatePipe, adjusted for ISO-8601:
import {DatePipe} from "#angular/common";
public rightWeekNum: number = 0;
constructor(private datePipe: DatePipe) { }
calcWeekOfTheYear(dateInput: Date) {
let falseWeekNum = parseInt(this.datePipe.transform(dateInput, 'ww'));
this.rightWeekNum = (dateInput.getDay() == 0) ? falseWeekNumber-1 : falseWeekNumber;
}

Inspired from RobG's answer.
What I wanted is the day of the week of a given date. So my answer is simply based on the day of the week Sunday. But you can choose the other day (i.e. Monday, Tuesday...);
First I find the Sunday in a given date and then calculate the week.
function getStartWeekDate(d = null) {
const now = d || new Date();
now.setHours(0, 0, 0, 0);
const sunday = new Date(now);
sunday.setDate(sunday.getDate() - sunday.getDay());
return sunday;
}
function getWeek(date) {
const sunday = getStartWeekDate(date);
const yearStart = new Date(Date.UTC(2021, 0, 1));
const weekNo = Math.ceil((((sunday - yearStart) / 86400000) + 1) / 7);
return weekNo;
}
// tests
for (let i = 0; i < 7; i++) {
let m = 14 + i;
let x = getWeek(new Date(2021, 2, m));
console.log('week num: ' + x, x + ' == ' + 11, x == 11, m);
}
for (let i = 0; i < 7; i++) {
let m = 21 + i;
let x = getWeek(new Date(2021, 2, m));
console.log('week num: ' + x, x + ' == ' + 12, x == 12, 'date day: ' + m);
}
for (let i = 0; i < 4; i++) {
let m = 28 + i;
let x = getWeek(new Date(2021, 2, m));
console.log('week num: ' + x, x + ' == ' + 13, x == 13, 'date day: ' + m);
}
for (let i = 0; i < 3; i++) {
let m = 1 + i;
let x = getWeek(new Date(2021, 3, m));
console.log('week num: ' + x, x + ' == ' + 13, x == 13, 'date day: ' + m);
}
for (let i = 0; i < 7; i++) {
let m = 4 + i;
let x = getWeek(new Date(2021, 3, m));
console.log('week num: ' + x, x + ' == ' + 14, x == 14, 'date day: ' + m);
}

now = new Date();
today = new Date(now.getFullYear(), now.getMonth(), now.getDate());
firstOfYear = new Date(now.getFullYear(), 0, 1);
numOfWeek = Math.ceil((((today - firstOfYear) / 86400000)-1)/7);

function getWeek(param) {
let onejan = new Date(param.getFullYear(), 0, 1);
return Math.ceil((((param.getTime() - onejan.getTime()) / 86400000) + onejan.getDay()) / 7);
}

Get next date from weekday in JavaScript

How can one return the next date of a given weekday (it could be either a number 0-6 or names Sunday-Saturday).
Example, if today, on Friday 16-Oct-2009 I passed in:
Friday, it would return today's date 16-Oct-2009
Saturday returns 17-Oct-2009
Thursday returns 22-Oct-2009

Just adding 7 doesn't solve the problem.
The below function will give you the next day of the week.
function nextDay(x){
var now = new Date();
now.setDate(now.getDate() + (x+(7-now.getDay())) % 7);
return now;
}

Here's a slightly modified version to Tim's answer to address the specific question-- pass in a date d, and, and a desired day of week (dow 0-6), return the date
function nextDay(d, dow){
d.setDate(d.getDate() + (dow+(7-d.getDay())) % 7);
return d;
}

Here is another simple solution
//takes dayIndex from sunday(0) to saturday(6)
function nextDate(dayIndex) {
var today = new Date();
today.setDate(today.getDate() + (dayIndex - 1 - today.getDay() + 7) % 7 + 1);
return today;
}
document.write("Next Sunday is: "+nextDate(0).toLocaleString()+"<br/>");
document.write("Next Thursday is: "+nextDate(4).toLocaleString()+"<br/>");
document.write("Next Saturday is: "+nextDate(6).toLocaleString());

And if you do not want do pass numbers but weekday-names (sunday - saturday) to find a future date of a certain weekday, then this helps you as well:
function getDateOfWeekday(refday){
var days = {
monday: 1,
tuesday: 2,
wednesday: 3,
thursday: 4,
friday: 5,
saturday: 6,
sunday: 0
};
if(!days.hasOwnProperty(refday))throw new Error(refday+" is not listed in "+JSON.stringify(days));
var currDate = new Date();
var currTimestamp = currDate.getTime();
var triggerDay = days[refday];
var dayMillDiff=0;
var dayInMill = 1000*60*60*24;
// add a day to dayMillDiff as long as the desired refday (sunday for instance) is not reached
while(currDate.getDay()!=triggerDay){
dayMillDiff += dayInMill;
currDate = new Date(currDate.getTime()+dayInMill);
}
return new Date(currTimestamp + dayMillDiff);
}
var sunday = getDateOfWeekday("sunday");
document.write("Next Sunday is at: <strong>"+sunday.toLocaleString()+"</strong><br/>");
var thursday = getDateOfWeekday("thursday");
thursday.setHours(0,0,0,0); // set hours/minutes/seconds and millseconds to zero
document.write("Next Thursday is at: <strong>"+thursday.toLocaleString()+"</strong> on midnight<br/>");
var tuesday = getDateOfWeekday("tuesday");
document.write("Next Tuesday is at: <strong>"+tuesday.toLocaleString()+"</strong><br/>");

To expand on user 190106's answer, this code should give you what you wanted:
function getNextDay(day, resetTime){
var days = {
sunday: 0, monday: 1, tuesday: 2,
wednesday: 3, thursday: 4, friday: 5, saturday: 6
};
var dayIndex = days[day.toLowerCase()];
if (dayIndex !== undefined) {
throw new Error('"' + day + '" is not a valid input.');
}
var returnDate = new Date();
var returnDay = returnDate.getDay();
if (dayIndex !== returnDay) {
returnDate.setDate(returnDate.getDate() + (dayIndex + (7 - returnDay)) % 7);
}
if (resetTime) {
returnDate.setHours(0);
returnDate.setMinutes(0);
returnDate.setSeconds(0);
returnDate.setMilliseconds(0);
}
return returnDate;
}
alert(getNextDay('thursday', true));

A swiss-knife tool for javascript DateTime programming.
http://www.datejs.com/

Categories