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How does momentjs handle addition or subtraction in terms of months or year

My question is how does momentjs handle addition or subtraction in terms months or years when there is a leap year or months that have different days in them such as March has 31 days and April has 30 days
An example is does it set it months to 30.4167 days by default or does it do some calculations on how many days will be in a month in different years or the difference of how many days there will be between March or April
moment().add(1, 'months'); is this equal to 30.4167 days for every month or 730.001 hours for every month?
How is momentjs handling this

Without moment.js, this solution seems to work well.
Basically set the month to the current month + the number of months.
One problem this causes is that adding 1 month to say 31st, and the next month only had 30, would give you the 1st of the next month.
To fix this, you can check for it. If the new day of the month is different to the original, then we overflowed and we can just set the day to 1 and subtract 1 day to handle this.
Below is an example, if you run you will also see 28 & 29 of Feb with the leap year difference.
const aday = 1000 * 60 * 60 * 24;
function addMonth(dt, m) {
const r = new Date(dt);
r.setMonth(r.getMonth() + m);
if (dt.getDate() !== r.getDate()) {
r.setDate(1);
r.setTime(r.getTime() - aday);
}
return r;
}
const first = new Date("2019-12-31");
for (let l = -10; l < 10; l += 1) {
const second = addMonth(first, l);
console.log(`${second.toDateString()} - ${l} months`);
}

var currentDate = moment('2015-11-31');
var addMonth = moment(currentDate).add(1, 'M');
for years
var addYear = moment(currentDate)..add('years', 1).format('L');

JS Check Date is Within 6 Months of Today

I am using Bootstrap Datepicker, and based on the date selection I need to display a message to the user.
I have never used the Date Constructor before so it's very new to me.
What I need to do is the following;
allow user to select a date
display a message / alert based of the logic below
If their selected date is within the last 6 months of today, they quality for discount.
If their selected date doesn't fall within the last 6 months of today, they don't.
Although it's not working correctly have created a fiddle here.
Any help would be appreciated. Code also below;
HTML
<input type="text" class="form-control" id="datepicker" placeholder="Year Graduated" value="" data-date-format="dd/mm/yyyy">
<p id="rate"></p>
JS
function compareDate() {
// get date from datepicker
var dateEntered = $("#datepicker").datepicker("getDate");
dateEntered = new Date(dateEntered).getTime();
//alert("date entered: " + dateEntered);
// set todays date
var now = new Date();
// set date six months before today
var sixMonthBeforeNow = new Date(now).setTime(now.getTime() - 3 * 28 * 24 * 60 * 60);
//alert("six months before: " + sixMonthBeforeNow);
// if date entered is within six months from today
if (dateEntered > sixMonthBeforeNow) {
alert("You qualify for the discount rate.");
$("#rate").html('discount rate');
}
// if date entered is over six months from today
if (dateEntered < sixMonthBeforeNow) {
alert("you graduated more than six months ago");
$("#rate").html('no discount');
}
}
$("#datepicker").datepicker({
weekStart: 1,
daysOfWeekHighlighted: "6,0",
autoclose: true,
todayHighlight: true
});
$("#datepicker").change(function() {
compareDate();
});
Note: I'd prefer not to use any other 3rd party JS library / plugin.

Just change your sixMonthBeforeNow with the below code, that should work.
var sixMonthBeforeNow = new Date(now).setMonth(now.getMonth() - 6);

You need to be careful with date arithmetic because it's not symmetric due to the uneven length of months, so you need rules to deal with it. E.g. what date is exactly 6 months before 31 August?
Before answering, consider:
28 February plus 6 months is 28 August
1 March plus 6 months is 1 September.
So what date is 6 months before 29, 30 and 31 August? Is it 28 February or 1 March?
Similar issues arise for any last day of a month where the month 6 months previous doesn't have 31 days. Should the limit be the 30th of the month or the 1st of the following month? When you've answered that question, then you can devise an algorithm to deliver the right answer and then the code to implement it.
If you want such cases to set the date to the end of the month 6 months before, then you can check the month resulting from subtracting 6 months and if it's not 6, set it to the last day of the previous month, e.g.
function sixMonthsPrior(date) {
// Copy date so don't affect original
var d = new Date(date);
// Get the current month number
var m = d.getMonth();
// Subtract 6 months
d.setMonth(d.getMonth() - 6);
// If the new month number isn't m - 6, set to last day of previous month
// Allow for cases where m < 6
var diff = (m + 12 - d.getMonth()) % 12;
if (diff < 6) d.setDate(0)
return d;
}
// Helper to format the date
function formatDate(d) {
return d.toLocaleString(undefined, {day:'2-digit', month:'short', year:'numeric'});
}
// Tests
[ new Date(2018, 7,31), // 31 Aug 2018
new Date(2018, 8, 1), // 1 Sep 2018
new Date(2018,11,31), // 31 Dec 2018
new Date(2019, 2,31) // 31 Mar 2019
].forEach( d => console.log(formatDate(d) + ' => ' + formatDate(sixMonthsPrior(d))));
If that is't the logic you wish to apply, you need to say what is.
PS. You can also implement the above logic by just comparing the start and end dates (day number). If they're different, it must have rolled over a month so set to 0.

exclude weekends in javascript date calculation

I have two sets of codes that work. Needed help combining them into one.
This code gets me the difference between two dates. works perfectly:
function test(){
var date1 = new Date(txtbox_1.value);
var date2 = new Date(txtbox_2.value);
var diff = (date2 - date1)/1000;
var diff = Math.abs(Math.floor(diff));
var days = Math.floor(diff/(24*60*60));
var leftSec = diff - days * 24*60*60;
var hrs = Math.floor(leftSec/(60*60));
var leftSec = leftSec - hrs * 60*60;
var min = Math.floor(leftSec/(60));
var leftSec = leftSec - min * 60;
txtbox_3.value = days + "." + hrs; }
source for the above code
The code below by #cyberfly appears to have the answer of excluding sat and sun which is what i needed. source. However, its in jquery and the above code is in JS. Therefore, needed help combining as i lacked that knowledge :(
<script type="text/javascript">
$("#startdate, #enddate").change(function() {
var d1 = $("#startdate").val();
var d2 = $("#enddate").val();
var minutes = 1000*60;
var hours = minutes*60;
var day = hours*24;
var startdate1 = getDateFromFormat(d1, "d-m-y");
var enddate1 = getDateFromFormat(d2, "d-m-y");
var days = calcBusinessDays(new Date(startdate1),new Date(enddate1));
if(days>0)
{ $("#noofdays").val(days);}
else
{ $("#noofdays").val(0);}
});
</script>
EDIT
Made an attempt at combining the codes. here is my sample. getting object expected error.
function test(){
var date1 = new Date(startdate.value);
var date2 = new Date(enddate.value);
var diff = (date2 - date1)/1000;
var diff = Math.abs(Math.floor(diff));
var days = Math.floor(diff/(24*60*60));
var leftSec = diff - days * 24*60*60;
var hrs = Math.floor(leftSec/(60*60));
var leftSec = leftSec - hrs * 60*60;
var min = Math.floor(leftSec/(60));
var leftSec = leftSec - min * 60;
var startdate1 = getDateFromFormat(startdate, "dd/mm/yyyy hh:mm");
var enddate1 = getDateFromFormat(enddate, "dd/mm/yyyy hh:mm");
days = calcBusinessDays(new Date(startdate1),new Date(enddate1));
noofdays.value = days + "." + hrs; }
start: <input type="text" id="startdate" name="startdate" value="02/03/2015 00:00">
end: <input type="text" id="enddate" name="enddate" value="02/03/2015 00:01">
<input type="text" id="noofdays" name="noofdays" value="">

When determining the number of days between two dates, there are lots of decisions to be made about what is a day. For example, the period 1 Feb to 2 Feb is generally one day, so 1 Feb to 1 Feb is zero days.
When adding the complexity of counting only business days, things get a lot tougher. E.g. Monday 2 Feb 2015 to Friday 6 February is 4 elapsed days (Monday to Tuesday is 1, Monday to Wednesday is 2, etc.), however the expression "Monday to Friday" is generally viewed as 5 business days and the duration Mon 2 Feb to Sat 7 Feb should also be 4 business days, but Sunday to Saturday should be 5.
So here's my algorithm:
Get the total number of whole days between the two dates
Divide by 7 to get the number of whole weeks
Multiply the number of weeks by two to get the number of weekend days
Subtract the number of weekend days from the whole to get business days
If the number of total days is not an even number of weeks, add the numbe of weeks * 7 to the start date to get a temp date
While the temp date is less than the end date:
if the temp date is not a Saturday or Sunday, add one the business days
add one to the temp date
That's it.
The stepping part at the end can probably be replaced by some other algorithm, but it will never loop for more than 6 days so it's a simple and reasonably efficient solution to the issue of uneven weeks.
Some consequences of the above:
Monday to Friday is 4 business days
Any day to the same day in a different week is an even number of weeks and therefore an even mutiple of 5, e.g. Monday 2 Feb to Monday 9 Feb and Sunday 1 Feb to Sunday 8 Feb are 5 business days
Friday 6 Feb to Sunday 7 Feb is zero business days
Friday 6 Feb to Monday 9 Feb is one business day
Sunday 8 Feb to: Sunday 15 Feb, Sat 14 Feb and Fri 13 Feb are all 5 business days
Here's the code:
// Expects start date to be before end date
// start and end are Date objects
function dateDifference(start, end) {
// Copy date objects so don't modify originals
var s = new Date(+start);
var e = new Date(+end);
// Set time to midday to avoid dalight saving and browser quirks
s.setHours(12,0,0,0);
e.setHours(12,0,0,0);
// Get the difference in whole days
var totalDays = Math.round((e - s) / 8.64e7);
// Get the difference in whole weeks
var wholeWeeks = totalDays / 7 | 0;
// Estimate business days as number of whole weeks * 5
var days = wholeWeeks * 5;
// If not even number of weeks, calc remaining weekend days
if (totalDays % 7) {
s.setDate(s.getDate() + wholeWeeks * 7);
while (s < e) {
s.setDate(s.getDate() + 1);
// If day isn't a Sunday or Saturday, add to business days
if (s.getDay() != 0 && s.getDay() != 6) {
++days;
}
}
}
return days;
}
I don't know how it compares to jfriend00's answer or the code you referenced, if you want the period to be inclusive, just add one if the start or end date are a business day.

Here's a simple function to calculate the number of business days between two date objects. As designed, it does not count the start day, but does count the end day so if you give it a date on a Tuesday of one week and a Tuesday of the next week, it will return 5 business days. This does not account for holidays, but does work properly across daylight savings changes.
function calcBusinessDays(start, end) {
// This makes no effort to account for holidays
// Counts end day, does not count start day
// make copies we can normalize without changing passed in objects
var start = new Date(start);
var end = new Date(end);
// initial total
var totalBusinessDays = 0;
// normalize both start and end to beginning of the day
start.setHours(0,0,0,0);
end.setHours(0,0,0,0);
var current = new Date(start);
current.setDate(current.getDate() + 1);
var day;
// loop through each day, checking
while (current <= end) {
day = current.getDay();
if (day >= 1 && day <= 5) {
++totalBusinessDays;
}
current.setDate(current.getDate() + 1);
}
return totalBusinessDays;
}
And, the jQuery + jQueryUI code for a demo:
// make both input fields into date pickers
$("#startDate, #endDate").datepicker();
// process click to calculate the difference between the two days
$("#calc").click(function(e) {
var diff = calcBusinessDays(
$("#startDate").datepicker("getDate"),
$("#endDate").datepicker("getDate")
);
$("#diff").html(diff);
});
And, here's a simple demo built with the date picker in jQueryUI: http://jsfiddle.net/jfriend00/z1txs10d/

const firstDate = new Date("December 30, 2020");
const secondDate = new Date("January 4, 2021");
const daysWithOutWeekEnd = [];
for (var currentDate = new Date(firstDate); currentDate <= secondDate; currentDate.setDate(currentDate.getDate() + 1)) {
// console.log(currentDate);
if (currentDate.getDay() != 0 && currentDate.getDay() != 6) {
daysWithOutWeekEnd.push(new Date(currentDate));
}
}
console.log(daysWithOutWeekEnd, daysWithOutWeekEnd.length);

#RobG has given an excellent algorithm to separate business days from weekends.
I think the only problem is if the starting days is a weekend, Saturday or Sunday, then the no of working days/weekends will one less.
Corrected code is below.
function dateDifference(start, end) {
// Copy date objects so don't modify originals
var s = new Date(start);
var e = new Date(end);
var addOneMoreDay = 0;
if( s.getDay() == 0 || s.getDay() == 6 ) {
addOneMoreDay = 1;
}
// Set time to midday to avoid dalight saving and browser quirks
s.setHours(12,0,0,0);
e.setHours(12,0,0,0);
// Get the difference in whole days
var totalDays = Math.round((e - s) / 8.64e7);
// Get the difference in whole weeks
var wholeWeeks = totalDays / 7 | 0;
// Estimate business days as number of whole weeks * 5
var days = wholeWeeks * 5;
// If not even number of weeks, calc remaining weekend days
if (totalDays % 7) {
s.setDate(s.getDate() + wholeWeeks * 7);
while (s < e) {
s.setDate(s.getDate() + 1);
// If day isn't a Sunday or Saturday, add to business days
if (s.getDay() != 0 && s.getDay() != 6) {
++days;
}
//s.setDate(s.getDate() + 1);
}
}
var weekEndDays = totalDays - days + addOneMoreDay;
return weekEndDays;
}
JSFiddle link is https://jsfiddle.net/ykxj4k09/2/

First Get the Number of Days in a month
totalDays(month, year) {
return new Date(year, month, 0).getDate();
}
Then Get No Of Working Days In A Month By removing Saturday and Sunday
totalWorkdays() {
var d = new Date(); // to know present date
var m = d.getMonth() + 1; // to know present month
var y = d.getFullYear(); // to knoow present year
var td = this.totalDays(m, y);// to get no of days in a month
for (var i = 1; i <= td; i++) {
var s = new Date(y, m - 1, i);
if (s.getDay() != 0 && s.getDay() != 6) {
this.workDays.push(s.getDate());// working days
}else {
this.totalWeekDays.push(s.getDate());//week days
}
}
this.totalWorkingDays = this.workDays.length;
}

I thought the above code snippets others shared are lengthy.
I am sharing a concise snippet that gives date after considering the total number of days specified. we can also customize dates other than Saturdays and Sundays.
function getBusinessDays(dateObj, days) {
for (var i = 0; i < days; i++) {
if (days > 0) {
switch (dateObj.getDay()) {
// 6 being Saturday and 0 being Sunday.
case 6, 0:
dateObj.setDate(dateObj.getDate() + 2)
break;
//5 = Friday.
case 5:
dateObj.setDate(dateObj.getDate() + 3)
break;
//handle Monday, Tuesday, Wednesday and Thursday!
default:
dateObj.setDate(dateObj.getDate() + 1)
//console.log(dateObj)
break;
}
}
}
return dateObj;
}
console.log(getBusinessDays(new Date(), 11))
//Mon Dec 20 2021 18:56:01 GMT+0530 (India Standard Time)

How to get difference between 2 Dates in Years, Months and days using moment.js

How to get difference between 2 Dates in Years, Months and days using moment.js?
For example the difference between 4/5/2014 & 2/22/2013 should be calculated as 1 Year, 1 Month and 14 Days.

Moment.js can't handle this scenario directly. It does allow you to take the difference between two moments, but the result is an elapsed duration of time in milliseconds. Moment does have a Duration object, but it defines a month as a fixed unit of 30 days - which we know is not always the case.
Fortunately, there is a plugin already created for moment called "Precise Range", which does the right thing. Looking at the source, it does something similar to torazaburo's answer - but it properly accounts for the number of days in the month to adjust.
After including both moment.js and this plugin (readable-range.js) in your project, you can simply call it like this:
var m1 = moment('2/22/2013','M/D/YYYY');
var m2 = moment('4/5/2014','M/D/YYYY');
var diff = moment.preciseDiff(m1, m2);
console.log(diff);
The output is "1 year 1 month 14 days"

You hardly need moment.
d1 = new Date(2014, 3, 5); // April 5, 2014
d2 = new Date(2013, 1, 22); // February 22, 2013
diff = new Date(
d1.getFullYear()-d2.getFullYear(),
d1.getMonth()-d2.getMonth(),
d1.getDate()-d2.getDate()
);
This takes advantage of the fact that the Date constructor is smart about negative values. For instance, if the number of months is negative, it will take that into account and walk back the year.
console.log(diff.getYear(), "Year(s),",
diff.getMonth(), "Month(s), and",
diff.getDate(), "Days.");
>> 1 Year(s), 1 Month(s), and 11 Days.
Your calculation is wrong--it's not 14 days, it's six remaining days in February and the first five days of April, so it's 11 days, as the computer correctly computes.
Second try
This might work better given #MattJohnson's comment:
dy = d1.getYear() - d2.getYear();
dm = d1.getMonth() - d2.getMonth();
dd = d1.getDate() - d2.getDate();
if (dd < 0) { dm -= 1; dd += 30; }
if (dm < 0) { dy -= 1; dm += 12; }
console.log(dy, "Year(s),", dm, "Month(s), and", dd, "Days.");

This worked for me. Verified with Age calculator.
function calculateAge(){
ageText = jQuery("#dob").closest(".form-group").find(".age-text");
ageText.text("");
level2.dob = jQuery("#dob").val();
if(!level2.dob) return;
level2.mdob= moment(level2.dob, 'DD-MM-YYYY');
if(!level2.mdob.isValid()){
alert("Invalid date format");
return;
}
level2.targetDate = moment();//TODO: Fill in the target date
level2.months = level2.targetDate.diff(level2.mdob, 'months'); // Calculate the months
let years = parseInt(level2.months/12); // A year has 12 months irrespective or leap year or not
let balanceMonths = level2.months%12; // The balance gives the number of months
let days;
if(!balanceMonths){ // If no balance months, then the date selected lies in the same month
months = 0; // so months = 0
days = level2.targetDate.diff(level2.mdob, 'days'); // only the days difference
}else{
months = balanceMonths;
dob_date = level2.mdob.date();
target_month = level2.targetDate.month();
construct_date = moment().month(target_month).date(dob_date);
days = level2.targetDate.diff(construct_date, 'days')+1; // There might be one day missed out. Not sure on UTC
}
ageText = years +" years " + months+ " months " + days +" days";
}

Problem with comparing dates in javascript

HI,
I have the following code that is supposed to compare two dates:
var d = ($('#day').val());
var m = ($('#month').val() -1);
var y = $('#year').val();
var birthdate = new Date(y,m,d);
alert('birthdate is' + birthdate);
var today = new Date();
alert('today is'+ today);
var diff = (today - birthdate);
years = Math.floor(diff/(1000*60*60*24*365));
alert(years);
It's basically working but I'm interested to see if the date of birth makes the user over 18 or not. So I've tried to put in 30th march 1993 - which would make the user 17. I'm alerting out the birthdate and it gives me back the correct date (mon mar 29 1993 00:00:00 GMT + 0100 BST)....however this is evaluating to 18 (alert(years) in the above code) when it should evaluate to seventeen. It's not until I put in 3rd April 1993 that it evaluates to 17.
Any ideas?

You have to mind leap-years, timezones... before reinventing the wheel, I recommend that you use DateJS.
if((18).years().ago().isBefore(birthdate)) {
// handle underage visitors
}

That's because you forgot the leap years.
These years had 366 days and occur usually every four years, so in any 18 years there are about four days more than 365*18, thus moving the neccessary start date four days ahead.
Probably in this case it is easier to check
if ((nowyear - birthyear > 18)
|| ((nowyear - birthyear == 18)&&(nowmonth - birthmonth > 0))
|| ((nowyear - birthyear == 18)&&(nowmonth == birthmonth)&&(nowday - birthday >= 0)))
// you're 18!

If you're looking for age, why not just go the simple route and deal with years, months, and days?
function findAge( birthday ){
var today = new Date();
var age = today.getFullYears() - birthday.getFullYears();
if( today.getMonth() - birthday.getMonth() < 0 ){
age--;
}
else if( today.getDay() - birthday.getDay() < 0 && today.getMonth() == birthday.getMonth() ){
age--;
}
}

try to take a look at this post