I am writing some javascript and came across moment library.I would like to use the moment to get the first Monday of 18 Month ago. How would I do it?
I know 18 months ago it is
moment().subtract(18, 'months');
But how would I know the first Monday of that time.
Thanks ahead of time!
You can do this in one line.
moment().subtract(18,'months').startOf('month').add(6 - moment().day("Monday").day() ,'days').startOf('week').day(1);
Find the moment 18 months ago, get the start date of that month, add 6 days since in worst case the first of that month is a tuesday(results in a date which is in the week that includes the first monday) and then get the start of that week.
Voila, all in one line.
1st edit: corrected the calculation to be locale independent and always return a Monday and not beginning of week since that is locale dependent.
2nd edit: locales makes it a bit more complicated. Adding 6 days to a Monday with a locale where the week ends on Saturday will move into another week thus we need to adapt the algorithm to take the Monday week number into consideration, i.e. subtract moment().day("Monday").day() which gives the locale dependent week day number of a Monday(0 or 1). Changed in the code above.
cleaner and more reusable IMHO ;)
var monday = moment().day('Monday').weekday();
var searchFirstMonday = moment().subtract(18, 'months').startOf('month');
while (searchFirstMonday.weekday() !== monday){
searchFirstMonday.add(1, 'day');
}
If you go back 18 months, get the first day of that month, then the Monday of that week, you'll get close:
moment().subtract(18, 'months').startOf('month').day(1)
To make sure the Monday is in the right month, you need to break that down a bit:
var month = moment().subtract(18, 'months');
var firstMonday = month.startOf('month').day(1);
if (firstMonday.month() != month.month()) {
firstMonday = firstMonday.add(7, 'days');
}
If anyone wants to do the same without any libraries.
Not sure if this is the best way to do it :P
var now = new Date();
//Get year and month
var month = now.getMonth();
var year = now.getFullYear();
//Months to go back
var monthsIntoPast = 18;
//Day of week we're looking for
var firstWeekDay= 2;
//Loop for one week
for(var x = 0; x < 7; x++) {
//Go back 18 months to first day + x of the month
var past = new Date(year, month - monthsIntoPast, 2 + x);
//First monday
if(past.getDay() == firstWeekDay) {
//First monday 18 months ago
alert(past.toUTCString())
break;
}
}
You use the following code to get what you need:
// Subtract 18 months from the current date, then get the first day of the month
var date = moment().subtract(18, 'months').startOf('month');
// Get current month
var month = date.month();
// Get monday of the first week of the month
var firstMonday = moment(date).weekday(0);
// Check if the first day of the month is not Monday
// and first monday of first week is in the desired month
if( date.weekday() != 0 && firstMonday.month() != month ){
// Add 1 week if needed
firstMonday.add(1, 'weeks');
}
The example above consideres Monday as the first day of the week. If Monday is not the first day of the week (day with index 0), you can get the correct index using moment.weekdays()
var moment = require('moment');
date = moment().subtract(18, 'months').startOf('month');
First we get the the current date and subtract 18 months. Then we find the start of the month, which as of today is
_d: Tue Jul 01 2014 00:00:00 GMT-0800 (AKDT),
So now we need to adjust for the next Monday. We get the current day of the week with date.day() which will give us a number between 0-7 with 0 being last Sunday and 7 being next Sunday. In this case, the first is on a Tuesday.
>date.day();
2
So we take the offset of the day of the week and subtract it from 8. Why 8 you say? Because if you count every number including 0 and 7 there are 8 numbers. (Think arrays)
//since it's not monday we add the offset
date = date.add(8-date.day(), 'days');
In your code you'd want to check if the First day returned actually IS a Monday so as to not get the second Monday of the month. So the whole thing might look like
date = moment().subtract(18, 'months').startOf('month');
if(date.day() > 1){ //check if it's Monday
//since it's not monday we add the offset
date = date.add(8-date.day(), 'days');
}
returns
_d: Mon Jul 07 2014 00:00:00 GMT-0800 (AKDT),
Related
I want to get the date for the next coming Sunday at 15:30 JST.
How to do that?
I got a string "Sunday 15:00 JST" and what I need to do is, convert that into the closest coming Sunday 15:00 JST and then turn all of that into Unix epoch time. I might run this code on any day of the week for any day of the week not just Sunday.
js
const currentDate = new Date();
// Sunday - Saturday : 0 - 6.
const currentDayOfWeek = currentDate.getDay();
// 1 - 31.
const currentDayOfMonth = currentDate.getDate();
// thursday would be: 7 - 4.
const daysUntilSunday = 7 - currentDayOfWeek;
// currentDayOfMonth + 7 would be the same day, but
// next week, then just subtract the difference between
// now and sunday.
const nextSunday = new Date().setDate(currentDayOfMonth + 7 - currentDayOfWeek);
const nextSundayAt3pm = new Date(nextSunday).setHours(15, 0, 0);
Moment.js
Using moment.js you can get and set the day of the week
https://momentjs.com/docs/#/get-set/day/
All you need to do is create a new Moment, then set the day to Sunday. But..
If the value given is from 0 to 6, the resulting date will be within the current (Sunday-to-Saturday) week.
Due to it recognising Sunday as the start of the week, you will need to get the Sunday at the start of the current week, then add 7 days on to the date to get the next Sunday from today.
In other words, you add 7 to the days.
// 0 - 6 sets it to a date of the week within the current week.
// if you provide a number greater than 6, it will bubble in to
// later weeks.
// i.e. 7 = 0 + 6 + 1. where 0 would be the previous Sunday, 6 would
// set it to Saturday of the current week, then adding an additional 1
// will set it to the Sunday of the next week.
const nextSunday = new moment(7); // sets the date to next Sunday.
// now just set the time to 3pm.
nextSunday.hour(15);
I have searched the web and found the script to get the week number in year. However my counting is difference. The below image is the week number I want to get. When I tested using '1/5/2015', my code got week number is 2, but the week number should be 1 in my requirement. Would someone can help me. Thanks in advance.
I found the javascript at IamSilviu/Get week number
There is my code:
function myWeekNumber(thisDate) {
var dt = new Date(thisDate)
var onejan=new Date(dt.getFullYear(), 0, 2);
return Math.ceil((((dt - onejan) / 86400000) + onejan.getDay() + 1) / 7); }
The algorithm you're trying to implement seems to be that:
Weeks start on Sunday
The first week of the year is the one that has any days in the year, e.g. 1 Jan 2016 was a Friday, so the first week of 2016 started on Sunday 27 December 2015
In this case, it's best to use UTC methods to avoid daylight saving issues:
function getWeekNumberNonISO(d) {
// Create UTC equivalent for 23:59:59.999 on the passed in date
var sat = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate(),23,59,59,999));
// Set to Saturday at end of week
sat.setUTCDate(sat.getUTCDate() + 6 - sat.getUTCDay());
// Get first day of year
var firstDay = new Date(Date.UTC(sat.getUTCFullYear(), 0, 1));
// Set to Sunday on or before, i.e. first day of first week in year
firstDay = firstDay.setUTCDate(firstDay.getUTCDate() - firstDay.getUTCDay());
// Week number is difference in dates divided by ms/week rounded
return Math.round((sat - firstDay)/(6.048e8));
}
// Get week number for Mon 5 Jan 2015
console.log(getWeekNumberNonISO(new Date(2015,0,5))); // 2
// Get week number for Sat 31 Dec 2011
console.log(getWeekNumberNonISO(new Date(2011,11,31))); //53
// Get week number for Sat 1 Jan 2011
console.log(getWeekNumberNonISO(new Date(2011,0,1))); // 1
// Get week number for Sun 2 Jan 2011
console.log(getWeekNumberNonISO(new Date(2011,0,2))); // 2
Js has function inbulid function which can be used to fetch the date from the given date of the week getweek().
var week=date.getWeek()
How to sellect all same weekdays by using momentJS? Ex: All Mondays of current month. If the day is 15th day of the month, there are two Mondays in that month, from 0 to 15th day of the month. Maybe it is some kind of looping, because momenthJS should return two dates-one for first Monday and second for second Monday in the given range and so on.
Or is there any other way to do this by using any other JavaScript library?
As you said a loop can solve this problem
move 4 weeks before from the date you have e.g. if we were on the last monday of the month we move to the first monday of the month or a previous date (if we move to the previous month we can still get the correct dates by doing more iterations)
get the month of the date you have (all the dates you get should have the same month)
move forward from the initial date computed above a week each time and check if the new date has the same month as the input date
function weekdaysFromMonth (date) {
// all the weekdays previous/next to date should be
// 7 days apart and also have the same month
var month = date.get('month')
// make sure that the start date is 4 weeks before now
// we might go to the previous month but anyway we'll
// get the correct dates by doing more iterations
var start = moment(date).subtract(4 * 7, 'days')
var dates = []
for (var i = 0; i < 10; i += 1) {
start.add(7, 'days')
if (start.get('month') === month) {
dates.push(moment(start))
}
}
return dates
}
document.write(
JSON.stringify(
weekdaysFromMonth(moment()), null, ' '
)
)
<script src="http://momentjs.com/downloads/moment.js"></script>
The moment.js library is awesome, and I use it almost all the time, but I recently ran into something interesting. I'm trying to plot data by week of the year, and one of the data points was 2013-12-31, moment.js tells me this is week 1? Is there a better way to handle this? either with 53, null, -1, or something?
moment('2013-12-31').week()
(returns) 1
I thought maybe using isoWeek or format would get around this, but they all return the same value of 1, despite the documentation saying it goes to 53.
moment('2013-12-31').isoWeek()
(returns) 1
+moment('2013-12-31').format('w')
(returns) 1
Anyone have any ideas on this? (short of making a test whether the week computed has a min/max date that covers the date value I passed it)
It is because the week from the 30th december 2013 is considered to be the 1st week of 2014 as you may see on this page epoch converter
And according to momentjs documentation:
The week with January 1st in it is the first week of the year.
I had a problem at my work where we used .format('YYYY WW') for some comparison logic.
That doesn't really make sense, as you should probably use .format('gggg WW') in such cases.
moment('2013-12-31').format('YYYY w'); // Returns 2013 1
moment('2013-12-31').format('gggg w'); // Returns 2014 1
https://momentjs.com/docs/#/displaying/format/
This is expected behavior. According to the ISO 8601 standard, 2013 is not a year with 53 weeks.
The long years, with 53 weeks in them, can be described by any of the following equivalent definitions:
any year starting on Thursday (dominical letter D or DC) and any leap year starting on Wednesday (ED)
any year ending on Thursday (D, ED) and any leap year ending on Friday (DC)
years in which 1 January and 31 December (in common years) or either (in leap years) are Thursdays
(source)
2013 started and ended on a Tuesday so therefore it is not a "long year" and 2013-12-31 is considered part of the first week of 2014.
If you want that week to be the 53rd, you'll have to write custom code for it as the ISO standard won't agree with you!
Moment.js docs aren't that straightforward with this I had to move from WW-YYYY to WW-GGGG
moment(2019-12-30T00:20:53.380Z).format(WW-YYYY) // Gave me 01-2019 incorrectly
moment(2019-12-30T00:20:53.380Z).format(WW-GGGG) // Gave me 01-2020 correctly
Findings
If your doing locale weeks, use ww & gggg
If your doing ISO weeks, use WW & GGGG
A mix of w/W & Y is incorrect usage
I had the same problem with the calculation of the week number, starting from the date of Sunday.
Finally I was able to solve the problem by calculating the week number starting not from Sunday but from Monday.
moment(date).isoWeekday(1).week()
Better right a custom method which will convert date into week and that can be customized easily.
//value : (MMM DD YYYY format)
function getEpiWeek(value) {
Date.prototype.getWeek = function () {
var target = new Date(this.valueOf());
// ISO week date weeks start on monday, so correct the day number
var dayNr = (this.getDay() + 7) % 7;
// Set the target to the thursday of this week so the
// target date is in the right year
target.setDate(target.getDate() - dayNr + 3);
// ISO 8601 states that week 1 is the week with january 4th in it
var jan4 = new Date(target.getFullYear(), 0, 4);
// Number of days between target date and january 4th
var dayDiff = (target - jan4) / 86400000;
if (new Date(target.getFullYear(), 0, 1).getDay() < 4) {
return 1 + Math.ceil(dayDiff / 7);
}
else { // jan 4th is on the next week (so next week is week 1)
return Math.ceil(dayDiff / 7);
}
};
var weekNumber = new Date(value).getWeek()
var year = getYear(value, weekNumber);
return weekNumber + ' ' + year;
}
function getYear(value, weekNumber) {
var year = parseInt(value.split(' ')[2]);
if (value.split(' ')[0] == 'Jan') {
if (weekNumber > 40) {
year = year - 1;
}
}
if (value.split(' ')[0] == 'Dec') {
if (weekNumber < 2) {
year = year + 1;
}
}
return year.toString();
}
Personally solved my ordering issue using :
if(d.month()==0) {
week = d.week();
}else{
week=d.isoWeek();
}
I really need some assistance with a time calculation in JS.
Put basically I need to calculate how many times a day of a month has occurred between two dates.
For Example -
A date of 15th of the month between 1st February 2014 to 14 May 2014 would be 3
A date of 15th of the month between 1st February 2014 to 16 May 2014 would be 4
I've looked at moment Jquery library but it estimates that a month is 30 days so I wouldn't be exact and take into consideration leap years - months with 28 days etc..
It really needs to be exact because its for a chargeable event calculation. The dates can spare many years so could lead to in-accuries because of the 30 day thing.
Any help would be appreciated
There are probably a million ways to do this... here's a brute force way:
// add a "addDays() method to Date"
Date.prototype.addDays = function(days)
{
var dat = new Date(this.valueOf());
dat.setDate(dat.getDate() + days);
return dat;
}
// provide two dates and a day ordinal you want to count between the two
function numOrdinalsBetweenDts(Date1, Date2, theOrdinal) {
var temp;
if(Date2 < Date1) { // put dates in the right order (lesser first)
temp = Date1;
Date1 = Date2;
Date2 = temp;
}
var workDate = Date1;
var ctr = 0;
while(workDate < Date2) { // iterate through the calendar until we're past the end
if(workDate.getDate() == theOrdinal) // if we match the ordinal, count it
ctr++;
workDate = workDate.addDays(1); // move the calendar forward a day
}
return ctr;
}
var result = numOrdinalsBetweenDts(new Date("July 21, 1901"), new Date("July 21, 2014"), 2);
console.log(result);
alert(result);
There is a slightly counter-intuitive behavior in the Javascript Date constructor where if you create a new Date with the day set to 0, it will assume the last day of the month. You can the use the following function get the number of days in a month:
function daysInMonth(month, year) {
return new Date(year, month, 0).getDate();
}
The Javascript date object is leap-year aware, so you can use this function reliably.
You then just need to count the number of months between the start and end date and check each one to make sure the day number is actually present in the month. You can short-circuit this check if the day is less than or equal to 28.