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I'm supposed to write a code for codewars to find out the number of times a month ends with a Friday within a range of years.
To start off, I did research and found out several solutions but I still couldn't figure out the results in the console.log.
The first solution is from this tutorial:
In this code, the solution is
let LastDay = new Date(1998, 5 + 1, 0).getDate();
I was able to get the date, but it wasn't clear which day the date falls upon.
Then I found another solution at w3schools. This solution also set the date to be the last day of this month:
var d = new Date();
d.setMonth(d.getMonth() +1, 0);
document.getElementById("demo").innerHTML = d;
However, it works if it displays it as innerHTML = Sat Nov 30 2019 00:57:09 GMT-0500 (Eastern Standard Time). However, when I tried to rewrite the code and console.log it like in this example:
let d = new Date();
let month = d.getMonth()+1;
let lastday = d.setMonth(month, 0);
console.log(lastday);
The result I got was 1575093343211. I don't understand how it displays those numbers instead of the dates I was expecting. I thought that if it does display the dates, starting with the day, I can convert the date to string or array and check if the first element is Friday and then add it to the counter in the code I'm writing. How do I get the code to display the way I want it to.
something like this will work...
function LastDayOfMonth(Year, Month) {
return new Date((new Date(Year, Month, 1)) - 1);
}
var d = LastDayOfMonth(new Date().getYear(), new Date().getMonth())
//var d = LastDayOfMonth(2009, 11)
var dayName = d.toString().split(' ')[0];
console.log(dayName)
The result I got was 1575093343211. I don't understand how it displays those numbers instead of the dates I was expecting
Because you console.log the output of the setMonth method, not the date object:
let lastday = d.setMonth(month, 0);
console.log(lastday);
According to the documentation, the setMonth method returns:
The number of milliseconds between 1 January 1970 00:00:00 UTC and the updated date.
Instead you should use that output to create a new instance of the date object:
let lastday = new Date(d.setMonth(month, 0));
console.log(lastday);
Algorithms to get the last day of the month are generally based on setting a date to day 0 of the following month, which ends up being the last day of the required month.
E.g. to get the last day for June, 2019 (noting that 6 is July, not June):
let endOfJune = new Date(2019, 6, 0):
Once you have the date, you can get the day where 0 is Sunday, 1 is Monday, etc. and 5 is Friday:
let endOfJuneDay = endOfJune.getDay();
The set* methods modify the Date they're called on and return the time value for the modified date. So you don't need to assign the result to anything:
let d = new Date();
let month = d.getMonth() + 1;
// Set date to the new month
d.setMonth(month, 0);
console.log(d);
So if you want to loop over the months for a range of years and get the number that end with a Friday (or any particular day), you might loop over the months something like:
/*
** #param {number} startYear - start year of range
** #param {number} endYear - end year of range
** #param {number} dat - day number, 0 = Sunday, 1 = Monday, etc.
** default is 0 (Sunday)
*/
function countEOMDay(startYear, endYear, day = 0) {
// startYear must be <= end year
if (startYear > endYear) return;
// Start on 31 Jan of start year
let start = new Date(startYear, 0, 31);
// End on 31 Dec of end year
let end = new Date(endYear, 11, 31);
let count = 0;
// Loop over months from start to end
while (start <= end) {
// Count matching days
if (start.getDay() == day) {
++count;
}
// Increment month to end of next month
start.setMonth(start.getMonth() + 2, 0);
}
return count;
}
console.log(countEOMDay(2019, 2019, 5)); // 1
console.log(countEOMDay(2018, 2019, 5)); // 3
You can use setMonth() method to set the month of a date object. The return value of setMonth() method is milliseconds between the date object and midnight January 1 1970. That's what you get from console.log(lastday);
Your return value,
1575093343211
is milliseconds between your date object (d) and midnight January 1 1970.
If you want to get the expected date, you have to console log your date object instead the lastday, as follows:
let d = new Date();
let month = d.getMonth()+1;
let lastday = d.setMonth(month, 0);
console.log(d);
output: Sat Nov 30 2019 00:02:47 GMT+0530 (India Standard Time)
This is an alternative solution I wrote to solve your problem. This will return the number of times a month ends with a Friday within a range of years. Hope this will help you :)
var days = [];
var count = 0;
function getLastFridaysCount(startYear, endYear) {
for (var year = startYear; year <= endYear; year++) {
days = [
31,
0 === year % 4 && 0 !== year % 100 || 0 === year % 400 ? 29 : 28,
31, 30, 31, 30, 31, 31, 30, 31, 30, 31
];
for (var month = 0; month <= 11; month++) {
var myDate = new Date();
myDate.setFullYear(year);
myDate.setMonth(month);
myDate.setDate(days[month]);
if(myDate.getDay() == 5)
{
count++;
}
}
}
return count;
}
console.log("count", getLastFridaysCount(2014, 2017));
this is the solution, in the code can find the comments "//" explaining of what happens in each iteration.
function lastDayIsFriday(initialYear, endYear) {
let count = 0;
//according to when the year ends starts the loop
if (endYear !== undefined) {
let start = new Date(initialYear, 0, 31);
let end = new Date(endYear, 11, 31);
while(start <= end) { //check if the start date is < or = to the end
//The getDay() method returns the day of the week (from 0 to 6) for the specified date.
if(start.getDay() === 5) { //if = to FriYAY!!!
count++; //count the day
}
start.setMonth(start.getMonth()+2, 0);// returns the month (from 0 to 11) .getMonth
} //& sets the month of a date object .setMonth
return count;
} else {
let start = new Date(initialYear, 0, 31);
console.log(start.toString());
for(let i = 0; i < 12; i++) {
if(start.getDay() === 5) {
count++;
}
start.setMonth(start.getMonth() + 2, 0);
// console.log(start.toString());
}
return count;
}
}
I want to calculate between two dates difference to percent. Only not date, hours needed to scale.
Example:
22-08-2017 09:00 start date,
30.09.2017 22:00 finish date,
The today date is 01.09.2017. When I look to system today, the application show to me "%47 percent completed" I want to this.
function getpercent(){
var strt = new Date(document.getElementById('start').value).getTime();
var end = new Date(document.getElementById('end').value).getTime();
var current = new Date(document.getElementById('current').value).getTime();
var completed = ((current - strt) / (end - strt)) * 100;
document.getElementById('percent').innerHTML = completed+"%";
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<p>start <input id="start" type="date" /></p>
<p>end <input id="end" type="date" /></p>
<p>current <input id="current" type="date" /></p>
<p>percent <span id="percent"></span></p>
<button onclick="getpercent()">get percent</button>
new Date() will take a date string and turn it into unix standard time as seconds.
The javascript Date object can be used in arithmetic expressions. It will convert to milliseconds.
var start, finish, midpoint, percent, elapsed;
start = new Date(2017, 8, 22, 9);
finish = new Date(2017, 9, 30, 22);
midpoint = new Date(2017, 8, 29, 12);
elapsed = midpoint - start;
percent = (elapsed / (finish - start)) * 100;
console.log('elapsed', elapsed, ' ms', percent, ' % complete');
https://jsfiddle.net/fwb3g4nc/1/
This is a simple class DiffTracker that accepts two dates in the constructor - start and end date and has one method getPercentage() that will return the percentage of hours passed from start date against the total hours between start and end date.
Let's see the following scenario:
Start Date = 2017-08-23 09:00
End Date = 2017-08-24 09:00
So now the total difference of hours is 24
If we call getPercentage() with date 2017-08-24 21:00 we should see result of 50%.
If we call getPercentage() with date 2017-08-24 03:00 we should see result of 75% because the difference is 18 hours
var diffTraker = new DiffTracker(new Date(2017, 7, 23, 9), new Date(2017, 7, 24, 9));
console.log('Start Date');
console.log(new Date(2017, 7, 23, 9));
console.log('-------------------');
console.log('End Date');
console.log(new Date(2017, 7, 24, 9));
console.log('-------------------');
console.log(diffTraker.getPercentage(new Date(2017, 7, 23, 21)) + '% from start date (' + new Date(2017, 7, 23, 21) + ')');
console.log(diffTraker.getPercentage(new Date(2017, 7, 24, 3)) + '% from start date (' + new Date(2017, 7, 24, 3) + ')');
console.log(diffTraker.getPercentage(new Date(2017, 7, 24, 5)) + '% from start date (' + new Date(2017, 7, 24, 5) + ')');
function DiffTracker(startDate, endDate){
var self = this;
self.start = startDate;
self.end = endDate;
self.totalHours = getDiffHours(self.start, self.end);
self.getPercentage = function(date){
var hoursFromStart = getDiffHours(self.start, date);
return (hoursFromStart * 100 / self.totalHours).toFixed(2);
}
function getDiffHours(start, end){
/* 36e5 is the scientific notation for 60*60*1000, dividing by which converts the milliseconds difference into hours */
return Math.abs(start - end) / 36e5;
}
}
$FirstDate = "22-08-2017 09:00";
$SecondDate = "23.09.2017 22:00";
Even if one day it shows 100%
In php i use this method:
<?php
$FirstDate = "22-08-2017 09:00";
$SecondDate = "30.09.2017 22:00";
$start = strtotime($FirstDate);
$finish = strtotime($SecondDate);
$diff = $finish - $start;
$progress = time() - $start; // You might have to modify the time function depending on where you live
$procent = ($progress / $diff) * 100;
$width = round($procent);
// The if statment below just makes sure that it does not show 110% for example.
if ($width >= 100)
{
echo "100 %";
}
else
{
echo $width;
}
Hope this helps!
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];
}
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);
}
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);
}