Develop Reference

How to manipulate date using Javascript

How can I achieve this sequence of date output if the user input is 04-29-2022 and the output is like this
What I want:
2022-05-14
2022-05-29
2022-06-14
2022-06-29
2022-07-14
2022-07-29
2022-08-14
2022-08-29
my code output
2022-05-13
2022-05-28
2022-06-12
2022-06-27
2022-07-12
2022-07-27
2022-08-11
2022-08-26
var dateRelease = new Date("04-29-2022")
const terms = 8
for (let i = 0; i < terms; i++) {
console.log(new Date(dateRelease.setDate(dateRelease.getDate() + 15)).toISOString().slice(0, 10))
}

Here is a function that takes the day of the month in the given date and determines which other date of the month would be needed in the output (either 15 more or 15 less). Then it generates dates alternating between those two date-of-the-month, and when it is the lesser of those two, incrementing the month. In case a date is invalid and automatically overflows into the next month, it is corrected to the last day of the intended month.
To format the date in the output, it is better to not use toISODateString as that interprets the date as a UTC Date, while new Date("2022-04-29") interprets the given string as a date in the local time zone. This can lead to surprises in some time zones. So I would suggest using toLocaleDateString with a locale that produces your desired format.
Here is the code:
function createSchedule(date, count) {
date = new Date(date);
let day = date.getDate();
let k = +(day > 15);
let days = k ? [day - 15, day] : [day, day + 15];
let result = [];
for (let i = 0; i < count; i++) {
k = 1 - k;
date.setDate(days[k]);
// When date overflows into next month, take last day of month
if (date.getDate() !== days[k]) date.setDate(0);
if (!k) date.setMonth(date.getMonth() + 1);
result.push(date.toLocaleDateString("en-SE"));
}
return result;
}
var dateRelease = new Date("2022-04-29");
var result = createSchedule(dateRelease, 25);
console.log(result);

var dateRelease = new Date("04-29-2022")
const terms = 8
for (let i = 0; i < terms; i++) {
let date = new Date(dateRelease.setDate(dateRelease.getDate() + 15)).toLocaleDateString('en-US');
let format = date.split('/').map(d => d.padStart(2 ,'0')).join('-')
console.log(format);
}

How to get all Saturdays in year with format as "Saturday, dd.MM.YYYY"?

I want to add all Saturdays of 2020/2021 into an object like following:
saturdays = {
"Saturday, 22.02.2020" : "Saturday, 22.02.2020" ,
"Saturday, 29.02.2020" : "Saturday, 29.02.2020"
}

1) First find out number of days in year (daysInYear method)
2) Find out first saturday date (firstSatDate method)
3) Go over for loop from first saturday to end of the year day and build the date string requirement format.
const daysInYear = year =>
(new Date(year + 1, 0, 1) - new Date(year, 0, 1)) / (24 * 60 * 60 * 1000);
const firstSatDate = year => {
const week_day = new Date(year, 0, 1).getDay();
const satDate = new Date(year, 0, 7 - week_day);
return satDate.getDate();
};
const getSaturdays = year => {
const yearDays = daysInYear(year);
const first = firstSatDate(year);
const saturdays = {};
for (let day = first; day <= yearDays; day = day + 7) {
const date = new Date(year, 0, day);
const day_str = String(date.getDate()).padStart(2, '0');
const month_str = String(date.getMonth() + 1).padStart(2, '0');
const date_str = `Saturday, ${day_str}.${month_str}.${date.getFullYear()}`;
saturdays[date_str] = date_str;
}
return saturdays;
};
console.log(getSaturdays(2020));
console.log(getSaturdays(2021));

It is an unusual format (name is the same as the value) and objects are not ordered so don't expect to get them back in any particular order . . . but it is pretty trivial to do if you want . . .
saturdays = {};
function loadSaturdays(startYear, endYear) {
const SATURDAY = 6;
let start = new Date("01/01/" + startYear);
let end = new Date("12/31/" + endYear);
var dateOptions = {weekday: 'long', year: 'numeric', month: 'numeric', day: 'numeric'};
var current = new Date(start);
while (current <= end) {
if (SATURDAY === current.getDay()) {
let newSaturday = "\"" + current.toLocaleString('en-GB', dateOptions).replace(/\//gi, '.') + "\"";
// if you want to see the individual ones as you are building the object
// console.log(newSaturday);
saturdays[newSaturday] = newSaturday;
}
current = new Date(current.setDate(current.getDate() + 1));
}
}
loadSaturdays("2020", "2021");
// if you want to see the entire object
//console.log(saturdays);
// objects are not ordered but they are all there
for (saturday in saturdays) {
console.log(saturday);
}

How can I use moment.js to add days, excluding weekends?

I'm setting a default follow-up date two days from current date, which currently works:
const Notify = moment().add(2, 'days').toDate();
However, I would like to exclude weekends. So I installed moment WeekDay, but I can't seem to get it to work with adding days to the current date. The documentation calls for:
moment().weekday(0)
But I can't get that to work with adding in two days forward. Any ideas?

This solution is simple, easy to follow, and works well for me:
function addBusinessDays(originalDate, numDaysToAdd) {
const Sunday = 0;
const Saturday = 6;
let daysRemaining = numDaysToAdd;
const newDate = originalDate.clone();
while (daysRemaining > 0) {
newDate.add(1, 'days');
if (newDate.day() !== Sunday && newDate.day() !== Saturday) {
daysRemaining--;
}
}
return newDate;
}

Try: moment-business-days
It should help you.
Example:
var momentBusinessDays = require("moment-business-days")
momentBusinessDays('20-09-2018', 'DD-MM-YYYY').businessAdd(3)._d
Result:
Tue Sep 25 2018 00:00:00 GMT+0530 (IST)

You could also not use external lib and do a simple function like one of these two:
const WEEKEND = [moment().day("Saturday").weekday(), moment().day("Sunday").weekday()]
const addBusinessDays1 = (date, daysToAdd) => {
var daysAdded = 0,
momentDate = moment(new Date(date));
while (daysAdded < daysToAdd) {
momentDate = momentDate.add(1, 'days');
if (!WEEKEND.includes(momentDate.weekday())) {
daysAdded++
}
}
return momentDate;
}
console.log(addBusinessDays1(new Date(), 7).format('MM/DD/YYYY'))
console.log(addBusinessDays1('09-20-2018', 3).format('MM/DD/YYYY'))
// This is the somewhat faster version
const addBusinessDays2 = (date, days) => {
var d = moment(new Date(date)).add(Math.floor(days / 5) * 7, 'd');
var remaining = days % 5;
while (remaining) {
d.add(1, 'd');
if (d.day() !== 0 && d.day() !== 6)
remaining--;
}
return d;
};
console.log(addBusinessDays2(new Date(), 7).format('MM/DD/YYYY'))
console.log(addBusinessDays2('09-20-2018', 3).format('MM/DD/YYYY'))
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>
They are slightly modified from this post and I think are a good alternative to external library you have to carry/deal with (assuming this is the only part you need and not other features of that lib).

This will do it based on any starting date, and without a costly loop. You calculate the number of weekend days you need to skip over, then just offset by the number of weekdays and weekends, together.
function addWeekdays(year, month, day, numberOfWeekdays) {
var originalDate = year + '-' + month + '-' + day;
var futureDate = moment(originalDate);
var currentDayOfWeek = futureDate.day(); // 0 = Sunday, 1 = Monday, ..., 6 = Saturday
var numberOfWeekends = Math.floor((currentDayOfWeek + numberOfWeekdays - 1) / 5); // calculate the number of weekends to skip over
futureDate.add(numberOfWeekdays + numberOfWeekends * 2, 'days'); // account for the 2 days per weekend
return futureDate;
}

const addWorkingDays = (date: Moment, days: number) => {
let newDate = date.clone();
for (let i = 0; i < days; i++) {
if (newDate.isoWeekday() !== 6 && newDate.isoWeekday() !== 7) {
newDate = newDate.add(1, "days");
} else {
newDate = newDate.add(1, "days");
i--;
}
}
return newDate.format("YYYY/MM/DD");
};

var moment = require("moment")
function addWorkingDay(date, days){
let daysToAdd = days
const today = moment(date);
const nextWeekStart = today.clone().add(1, 'week').weekday(1);
const weekEnd = today.clone().weekday(5);
const daysTillWeekEnd = Math.max(0, weekEnd.diff(today, 'days'));
if(daysTillWeekEnd >= daysToAdd) return today.clone().add(daysToAdd, 'days');
daysToAdd = daysToAdd - daysTillWeekEnd - 1;
return nextWeekStart.add(Math.floor(daysToAdd/5), 'week').add(daysToAdd % 5, 'days')
}

I think this code will be faster:
var businessDays = 10;
var days = businessDays + Math.floor((Math.min(moment().day(),5)+businessDays)/6)*2;
moment.add(days, 'days');

// using pure JS
function addBusinessDays(originalDate, numDaysToAdd) {
const Sunday = 0;
const Saturday = 6;
let daysRemaining = numDaysToAdd;
const newDate = originalDate;
while (daysRemaining > 0) {
newDate.setDate(newDate.getDate() + 1);
if (newDate.getDay() !== 0 && newDate.getDay() !== 6) {
// skip sunday & saturday
daysRemaining--;
}
}
return newDate;
}
var dt = new Date(); // get date
var business_days = 8;
newDate = addBusinessDays(dt, business_days);
console.log(newDate.toString());

Get all days of the week given a day

I'm trying to make a function to get all the days of the week given the current day. I had a function that i thought was working until i noticed that if the day of the week is near the end of the month, like for example February, i get weird data. Anyone know whats going on and how to fix it?
function days(current) {
var week = new Array();
// Starting Monday not Sunday
var first = ((current.getDate() - current.getDay()) + 1);
for (var i = 0; i < 7; i++) {
week.push(
new Date(current.setDate(first++))
);
}
return week;
}
var input = new Date(2017, 1, 27);
console.log('input: %s', input);
var result = days(input);
console.log(result.map(d => d.toString()));
.as-console-wrapper{min-height:100%}

If you don't want to use some kind of other library like Moment.js you can also change your function a little and then it will work. Try this:
function dates(current) {
var week= new Array();
// Starting Monday not Sunday
current.setDate((current.getDate() - current.getDay() +1));
for (var i = 0; i < 7; i++) {
week.push(
new Date(current)
);
current.setDate(current.getDate() +1);
}
return week;
}
console.log(dates(new Date(2017, 1, 27)));

You can use Moment.js library - utility library for dates/time operations
Here's examplary code to get current week's dates starting from monday:
function getThisWeekDates() {
var weekDates= [];
for (var i = 1; i <= 7; i++) {
weekDates.push(moment().day(i));
}
return weekDates;
}
var thisWeekDates = getThisWeekDates();
thisWeekDates.forEach(function(date){ console.log(date.format());});
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.js"></script>
The code above prints following results to the console:
2017-03-20T21:26:27+01:00
2017-03-21T21:26:27+01:00
2017-03-22T21:26:27+01:00
2017-03-23T21:26:27+01:00
2017-03-24T21:26:27+01:00
2017-03-25T21:26:27+01:00
2017-03-26T21:26:27+02:00

I will trace your code using your example of Feb 27, 2017:
first = 27 - 1 + 1 = 27
loop:
Feb.setDate(27) = 27 feb
Feb.setDate(28) = 28 feb
Feb.setDate(29) = Not 29 days in Feb. So it sets current to 29-28 = 1st day of March
March.setDate(30) = March 30
March.setDate(31) = March 31
March.setDate(32) = Not 32 days in March. So it sets current to 31-32 = 1st of April..
April.setDate(33) = Not 33 days in April. So it sets current day 33-30 = 3rd day of May.
Please note that I used the shorthand of Month.setDate() to show the month of the current Date object when it was being called.
So the issue is with your understanding of setDate that is being used on current. It changes the month and if the value you use isn't a day in the month it adjusts the month and day appropriately. I hope this cleared things up for you.
For how to add one to a date, see Add +1 to current date. Adapted to your code, you can set current to the first day of the week then just keep adding 1 day and pushing copies to the array:
function days(current) {
var week = [];
// Starting Monday not Sunday
var first = current.getDate() - current.getDay() + 1;
current.setDate(first);
for (var i = 0; i < 7; i++) {
week.push(new Date(+current));
current.setDate(current.getDate()+1);
}
return week;
}
var input = new Date(2017, 1, 27);
console.log('input: %s', input);
var result = days(input);
console.log(result.map(d => d.toString()));
Note that this changes the date passed in (per the original code), you may want to make current a copy to avoid that.

Suppose monday starts the week, you can calculate monday and go to sunday. getDategives you the day of the week, and Sunday starts at 0. With momnday, we get just offset forward to 6 days to get sunday
mondayThisWeek(date: Date): Date {
const d = new Date(date)
const day = d.getDay()
const diff = d.getDate() - day + (day === 0 ? -6 : 1)
return new Date(d.setDate(diff))
}
const offsetDate = (base: Date, count: number): Date => {
const date = new Date(base)
date.setDate(base.getDate() + count)
return date
}
thisWeek(today: Date): TimeRange {
const monday = mondayThisWeek(today)
return {
startDate: monday,
endDate: offsetDate(monday, 6)
}
}

This can be achieved easly using moment
const getWeekDates = () => {
let weekDates = [];
for (let i = 0; i < 7; i++)
weekDates.push(moment().add(i, 'd'));
return weekDates;
};
console.log(getWeekDates());
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.js"></script>

How to calculate the last friday of the month with momentjs

How could I calculate the last friday of this month using the momentjs api?

Correct answer to this question:
var lastFriday = function () {
var lastDay = moment().endOf('month');
if (lastDay.day() >= 5)
var sub = lastDay.day() - 5;
else
var sub = lastDay.day() + 2;
return lastDay.subtract(sub, 'days');
}
The previous answer returns the next to last friday if the last day of the month is friday.

Given a moment in the month you want the last Friday for:
var lastFridayForMonth = function (monthMoment) {
var lastDay = monthMoment.endOf('month').startOf('day');
switch (lastDay.day()) {
case 6:
return lastDay.subtract(1, 'days');
default:
return lastDay.subtract(lastDay.day() + 2, 'days');
}
},
E.g.
// returns moment('2014-03-28 00:00:00');
lastFridayForMonth(moment('2014-03-14));

Sorry guys but I tested previous answers and all of them are wrong.
Check all of them for
moment([2017,2])
And you will find that the result is incorrect.
I wrote this solution which is working so far:
let date = moment([2017,2]).endOf('month');
while (date.day() !== 5) {
date.subtract(1,'days')
}
return date;

Shorter answer :
var lastFridayForMonth = function (monthMoment) {
let lastDay = monthMoment.endOf('month').endOf('day');
return lastDay.subtract((lastDay.day() + 2) % 7, 'days');
}

I tried testing multiple months and for few months above answer by #afternoon did not work. Below is the test code.(one such test is for Aug 2018)
var moment = require('moment')
var affirm = require("affirm.js")
var cc = moment(Date.now())
for (var i = 0; i < 100000; i++) {
lastFridayForMonth(cc)
var nextWeek = moment(cc).add(7, 'days')
console.log(cc.format("ddd DD MMM YYYY"), nextWeek.format('MMM'))
affirm((cc.month() - nextWeek.month()) === -1 || (cc.month() - nextWeek.month()) === 11, "1 month gap is not found")
affirm(cc.day() === 5, "its not friday")
cc.add(1, "months")
}
I have put another solution
function lastFridayForMonth(monthMoment) {
var month = monthMoment.month()
monthMoment.endOf("month").startOf("isoweek").add(4, "days")
if (monthMoment.month() !== month) monthMoment.subtract(7, "days")
}