Javascript - Previous month computation from a current date - javascript

I have a below JS where I get the max date that is user allowed to enter from a backend script:
var max_date = new Date(pdate + " " + ptime);
where pdate and ptime is fetched from a script.
Now I need to set the min date as 1 month less than max_date
if (max_date.getMonth() == 0)
subtractyear = 1;
var min_date = new Date(Date.UTC(max_date.getFullYear() - subtractyear,max_date.getMonth() - 1,max_date.getDate(),max_date.getHours(),0,0));
My issue is that if max_date is March 31 - then will the min_date be rolled over to Feb 28 or Feb 29 or Feb 31 or Feb 30?
If the date formed is an incorrect date - say Feb 30 how can I rectify this?


Simple subject the month by 1 would get a valid date -- never would setMonth method return an invalid Date object (the same as setDate, setYear and the Date constructor):
var date = new Date(2012, 02, 31); // 2012-03-31
date.setMonth(date.getMonth() - 1); // This gets 2012-03-02
I don't quite clear what date you expected, the last day of the previous month or just the day one month earlier?

Related

End of Month using javascript [duplicate]

If you provide 0 as the dayValue in Date.setFullYear you get the last day of the previous month:
d = new Date(); d.setFullYear(2008, 11, 0); // Sun Nov 30 2008
There is reference to this behaviour at mozilla. Is this a reliable cross-browser feature or should I look at alternative methods?

var month = 0; // January
var d = new Date(2008, month + 1, 0);
console.log(d.toString()); // last day in January
IE 6: Thu Jan 31 00:00:00 CST 2008
IE 7: Thu Jan 31 00:00:00 CST 2008
IE 8: Beta 2: Thu Jan 31 00:00:00 CST 2008
Opera 8.54: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.27: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.60: Thu Jan 31 2008 00:00:00 GMT-0600
Firefox 2.0.0.17: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Firefox 3.0.3: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Google Chrome 0.2.149.30: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Safari for Windows 3.1.2: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Output differences are due to differences in the toString() implementation, not because the dates are different.
Of course, just because the browsers identified above use 0 as the last day of the previous month does not mean they will continue to do so, or that browsers not listed will do so, but it lends credibility to the belief that it should work the same way in every browser.

I find this to be the best solution for me. Let the Date object calculate it for you.
var today = new Date();
var lastDayOfMonth = new Date(today.getFullYear(), today.getMonth()+1, 0);
Setting day parameter to 0 means one day less than first day of the month which is last day of the previous month.

I would use an intermediate date with the first day of the next month, and return the date from the previous day:
int_d = new Date(2008, 11+1,1);
d = new Date(int_d - 1);

In computer terms, new Date() and regular expression solutions are slow! If you want a super-fast (and super-cryptic) one-liner, try this one (assuming m is in Jan=1 format). I keep trying different code changes to get the best performance.
My current fastest version:
After looking at this related question Leap year check using bitwise operators (amazing speed) and discovering what the 25 & 15 magic number represented, I have come up with this optimized hybrid of answers (note the parameters m & y must obviously be integers for this to work):
function getDaysInMonth(m, y) {
return m===2 ? y & 3 || !(y%25) && y & 15 ? 28 : 29 : 30 + (m+(m>>3)&1);
}
Given the bit-shifting this obviously assumes that your m & y parameters are both integers, as passing numbers as strings would result in weird results.
JSFiddle: http://jsfiddle.net/TrueBlueAussie/H89X3/22/
JSPerf results: http://jsperf.com/days-in-month-head-to-head/5
For some reason, (m+(m>>3)&1) is more efficient than (5546>>m&1) on almost all browsers.
The only real competition for speed is from #GitaarLab, so I have created a head-to-head JSPerf for us to test on: http://jsperf.com/days-in-month-head-to-head/5
It works based on my leap year answer here: javascript to find leap year this answer here Leap year check using bitwise operators (amazing speed) as well as the following binary logic.
A quick lesson in binary months:
If you interpret the index of the desired months (Jan = 1) in binary you will notice that months with 31 days either have bit 3 clear and bit 0 set, or bit 3 set and bit 0 clear.
Jan = 1 = 0001 : 31 days
Feb = 2 = 0010
Mar = 3 = 0011 : 31 days
Apr = 4 = 0100
May = 5 = 0101 : 31 days
Jun = 6 = 0110
Jul = 7 = 0111 : 31 days
Aug = 8 = 1000 : 31 days
Sep = 9 = 1001
Oct = 10 = 1010 : 31 days
Nov = 11 = 1011
Dec = 12 = 1100 : 31 days
That means you can shift the value 3 places with >> 3, XOR the bits with the original ^ m and see if the result is 1 or 0 in bit position 0 using & 1. Note: It turns out + is slightly faster than XOR (^) and (m >> 3) + m gives the same result in bit 0.
JSPerf results: http://jsperf.com/days-in-month-perf-test/6

My colleague stumbled upon the following which may be an easier solution
function daysInMonth(iMonth, iYear)
{
return 32 - new Date(iYear, iMonth, 32).getDate();
}
stolen from http://snippets.dzone.com/posts/show/2099

A slight modification to solution provided by lebreeze:
function daysInMonth(iMonth, iYear)
{
return new Date(iYear, iMonth, 0).getDate();
}

I recently had to do something similar, this is what I came up with:
/**
* Returns a date set to the begining of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function beginningOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1)
date.setHours(0);
date.setMinutes(0);
date.setSeconds(0);
return date;
}
/**
* Returns a date set to the end of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function endOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1); // Avoids edge cases on the 31st day of some months
date.setMonth(date.getMonth() +1);
date.setDate(0);
date.setHours(23);
date.setMinutes(59);
date.setSeconds(59);
return date;
}
Pass it in a date, and it will return a date set to either the beginning of the month, or the end of the month.
The begninngOfMonth function is fairly self-explanatory, but what's going in in the endOfMonth function is that I'm incrementing the month to the next month, and then using setDate(0) to roll back the day to the last day of the previous month which is a part of the setDate spec:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/setDate
https://www.w3schools.com/jsref/jsref_setdate.asp
I then set the hour/minutes/seconds to the end of the day, so that if you're using some kind of API that is expecting a date range you'll be able to capture the entirety of that last day. That part might go beyond what the original post is asking for but it could help someone else looking for a similar solution.
Edit: You can also go the extra mile and set milliseconds with setMilliseconds() if you want to be extra precise.

How NOT to do it
Beware of any answers for the last of the month that look like this:
var last = new Date(date)
last.setMonth(last.getMonth() + 1) // This is the wrong way to do it.
last.setDate(0)
This works for most dates, but fails if date is already the last day of the month, on a month that has more days than the following month.
Example:
Suppose date is 07/31/21.
Then last.setMonth(last.getMonth() + 1) increments the month, but keeps the day set at 31.
You get a Date object for 08/31/21,
which is actually 09/01/21.
So then last.setDate(0) results in 08/31/21 when what we really wanted was 07/31/21.

try this one.
lastDateofTheMonth = new Date(year, month, 0)
example:
new Date(2012, 8, 0)
output:
Date {Fri Aug 31 2012 00:00:00 GMT+0900 (Tokyo Standard Time)}

This works for me.
Will provide last day of given year and month:
var d = new Date(2012,02,0);
var n = d.getDate();
alert(n);

This one works nicely:
Date.prototype.setToLastDateInMonth = function () {
this.setDate(1);
this.setMonth(this.getMonth() + 1);
this.setDate(this.getDate() - 1);
return this;
}

You can get the First and Last Date in the current month by following the code:
var dateNow = new Date();
var firstDate = new Date(dateNow.getFullYear(), dateNow.getMonth(), 1);
var lastDate = new Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0);
or if you want to format the date in your custom format then you can use moment js
var dateNow= new Date();
var firstDate=moment(new Date(dateNow.getFullYear(),dateNow.getMonth(), 1)).format("DD-MM-YYYY");
var currentDate = moment(new Date()).format("DD-MM-YYYY"); //to get the current date var lastDate = moment(new
Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0)).format("DD-MM-YYYY"); //month last date

This will give you current month first and last day.
If you need to change 'year' remove d.getFullYear() and set your year.
If you need to change 'month' remove d.getMonth() and set your year.
var d = new Date();
var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
var fistDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth(), 1).getDay())];
var LastDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth() + 1, 0).getDay())];
console.log("First Day :" + fistDayOfMonth);
console.log("Last Day:" + LastDayOfMonth);
alert("First Day :" + fistDayOfMonth);
alert("Last Day:" + LastDayOfMonth);

Try this:
function _getEndOfMonth(time_stamp) {
let time = new Date(time_stamp * 1000);
let month = time.getMonth() + 1;
let year = time.getFullYear();
let day = time.getDate();
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
day = 31;
break;
case 4:
case 6:
case 9:
case 11:
day = 30;
break;
case 2:
if (_leapyear(year))
day = 29;
else
day = 28;
break
}
let m = moment(`${year}-${month}-${day}`, 'YYYY-MM-DD')
return m.unix() + constants.DAY - 1;
}
function _leapyear(year) {
return (year % 100 === 0) ? (year % 400 === 0) : (year % 4 === 0);
}

const today = new Date();
let beginDate = new Date();
let endDate = new Date();
// fist date of montg
beginDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 1}-01 00:00:00`
);
// end date of month
// set next Month first Date
endDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 2}-01 :23:59:59`
);
// deducting 1 day
endDate.setDate(0);

Below function gives the last day of the month :
function getLstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 0).getDate()
}
console.log(getLstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 29
console.log(getLstDayOfMonFnc(new Date(2017, 2, 15))) // Output : 28
console.log(getLstDayOfMonFnc(new Date(2017, 11, 15))) // Output : 30
console.log(getLstDayOfMonFnc(new Date(2017, 12, 15))) // Output : 31
Similarly we can get first day of the month :
function getFstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 1).getDate()
}
console.log(getFstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 1

Here is an answer that conserves GMT and time of the initial date
var date = new Date();
var first_date = new Date(date); //Make a copy of the date we want the first and last days from
first_date.setUTCDate(1); //Set the day as the first of the month
var last_date = new Date(first_date); //Make a copy of the calculated first day
last_date.setUTCMonth(last_date.getUTCMonth() + 1); //Add a month
last_date.setUTCDate(0); //Set the date to 0, this goes to the last day of the previous month
console.log(first_date.toJSON().substring(0, 10), last_date.toJSON().substring(0, 10)); //Log the dates with the format yyyy-mm-dd

function getLastDay(y, m) {
return 30 + (m <= 7 ? ((m % 2) ? 1 : 0) : (!(m % 2) ? 1 : 0)) - (m == 2) - (m == 2 && y % 4 != 0 || !(y % 100 == 0 && y % 400 == 0));
}

set month you need to date and then set the day to zero ,so month begin in 1 - 31 in date function then get the last day^^
var last = new Date(new Date(new Date().setMonth(7)).setDate(0)).getDate();
console.log(last);

I know it's just a matter of semantics, but I ended up using it in this form.
var lastDay = new Date(new Date(2008, 11+1,1) - 1).getDate();
console.log(lastDay);
Since functions are resolved from the inside argument, outward, it works the same.
You can then just replace the year, and month / year with the required details, whether it be from the current date. Or a particular month / year.

If you need exact end of the month in miliseconds (for example in a timestamp):
d = new Date()
console.log(d.toString())
d.setDate(1)
d.setHours(23, 59, 59, 999)
d.setMonth(d.getMonth() + 1)
d.setDate(d.getDate() - 1)
console.log(d.toString())

The accepted answer doesn't work for me, I did it as below.
$( function() {
$( "#datepicker" ).datepicker();
$('#getLastDateOfMon').on('click', function(){
var date = $('#datepicker').val();
// Format 'mm/dd/yy' eg: 12/31/2018
var parts = date.split("/");
var lastDateOfMonth = new Date();
lastDateOfMonth.setFullYear(parts[2]);
lastDateOfMonth.setMonth(parts[0]);
lastDateOfMonth.setDate(0);
alert(lastDateOfMonth.toLocaleDateString());
});
});
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<link rel="stylesheet" href="/resources/demos/style.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
</head>
<body>
<p>Date: <input type="text" id="datepicker"></p>
<button id="getLastDateOfMon">Get Last Date of Month </button>
</body>
</html>

This will give you last day of current month.
notes: on ios device include time.
#gshoanganh
var date = new Date();
console.log(new Date(date.getFullYear(), date.getMonth() + 1, 0, 23, 59, 59));

if you just need to get the last date of a month following worked out for me.
var d = new Date();
const year = d.getFullYear();
const month = d.getMonth();
const lastDay = new Date(year, month +1, 0).getDate();
console.log(lastDay);
try it out here https://www.w3resource.com/javascript-exercises/javascript-date-exercise-9.php

In my case, this code was useful
end_date = new Date(2018, 3, 1).toISOString().split('T')[0]
console.log(end_date)

Subtracting 1 month to 2015-12-31 gives 2015-12-01

I'm trying to subtract one month from 2015-12-31 but it gives me 2015-12-01 instead of 2015-11-30. Why ?
Code:
var date1 = new Date('2015-12-31');
var date2 = new Date(date1);
date2.setMonth(date1.getMonth() - 1);
console.log(date1);
console.log(date2);
Output:
Thu Dec 31 2015 01:00:00 GMT+0100 (CET)
Tue Dec 01 2015 01:00:00 GMT+0100 (CET)
Any workaround?

When subtracting months, you can check whether the day of the adjusted Date is different to the day of the initial Date. If it is, then it must have rolled over to the next month, so set the day of the adjusted Date to 0, so it goes to the last day of the previous month, e.g.
function subtractMonths(date, months) {
var day = date.getDate();
date.setMonth(date.getMonth() - months);
if (date.getDate() != day) date.setDate(0);
return date;
}
// 31 Mar 2016 - 1 month = 29 Feb 2015
[[new Date(2016,2,31), 1],
// 29 Feb 2016 - 12 months = 28 Feb 2015
[new Date(2016,1,29), 12],
// 15 Feb 2016 - 3 months = 15 Nov 2015
[new Date(2016,1,15), 3]].forEach(function(arr){
document.write('<br>' + subtractMonths(arr[0], arr[1]));
})
The same algorithm can be used for adding months. Note that this is why date arithmetic is not symmetric, e.g.
31 May + 1 month => 30 June
30 June - 1 month => 30 May
i.e. If A + B = C, then C - B = A may or may not be true (and vice versa).

Try this
var date1 = new Date('2015-12-31');
var date2 = new Date(date1);
date2.setDate(date2.getDate()-date1.getDate());
alert(date2)

Per the setMonth documentation, ‘If you do not specify the [optional] dayValue parameter, the value returned from the getDate() method is used’. Since you’re not specifying the optional parameter, your code tries to set the date to 2015-11-31, which isn’t valid. JavaScript resolves this situation by setting the date to one day after 2015-11-30, which is 2015-12-01.
As for a workaround, it depends on what you’re actually trying to do. Are you trying to go 31 days back from 31 December? Or are you trying to get the last day of the month before December? Date semantics are extremely complicated; what are you going to do when the inevitable edge cases arise?

It is producing the requested result, which is subtracting 1 month from the date given. But remember a month is a variable amount of time. November 31 is actually December 1 (just like November 55th would actually be December 25, Christmas). To get the last day of the previous month you could do something like this:
var date = new Date('2015-12-31');
date.setDate(-1)

Are there any JavaScript methods that can replicate the Oracle's ADD_MONTH() functionality

1) Oracle's example of ADD_MONTHS(date, 1):
SELECT ADD_MONTHS('30-Nov-15', 3) FROM dual;
February, 29 2016 00:00:00
2) JavaScript:
var date= new Date("Mon Nov 30 2015 00:00:00");
date.setMonth(date.getMonth() + 3);
Tue Mar 01 2016 00:00:00
Are there any JavaScript methods that can replicate the Oracle's ADD_MONTH() functionality ?

If you want to implement the same logik as in Oracle function - i.e. for "shorter" month you do not overflow in the next month, I guess you will need to do it yourself:
Pseudocode:
myDay = date.getDate(); // save the date
date.setMonth(date.getMonth() + 3); // add months
myNewDay = date.getDate();
while (myDay != myNewDay & myNewDay <= 3) {
myNewDay = myNewDay -1 // go back one day
date.setDate(myNewDay); // restore the
}
So if you end with the same day of the month after adding months you are ready.
If you get a different day of month, it will be 1,2 or 3 (the difference in month length);
go back day by day until you reach the end of the month.
This is my knowledge of the Oracle algorithm. HTH.

date.getMonth()
returns the previous months date instead of this months date. So to add to the correct date just do
date.setMonth(date.getMonth() + 2);

Different ways to initialize Javascript Date object and getting different results each way [duplicate]

Why do these two dates are differents :
var date1 = new Date();
date1.setFullYear(2012); // year (four digits)
date1.setMonth(10); // month (from 0-11)
date1.setDate(1); // day of the month (from 1-31)
var date2 = new Date(2012, 10, 1, 0, 0, 0, 0);
Result :
Date 1 : Sat Dec 01 2012 14:56:16 GMT+0100
Date 2 : Thu Nov 01 2012 00:00:00 GMT+0100
whereas these two dates are equals :
var date3 = new Date();
date3.setFullYear(2012); // year (four digits)
date3.setMonth(9); // month (from 0-11)
date3.setDate(1); // day of the month (from 1-31)
var date4 = new Date(2012, 9, 1, 0, 0, 0, 0);
Result :
Date 3 : Mon Oct 01 2012 14:56:16 GMT+0200
Date 4 : Mon Oct 01 2012 00:00:00 GMT+0200
Another question is why do date1.setMonth(10) gives a date in December (should be November).

Finally got it. new Date() sets the date to the current date and time. In other words, October 31st (at the time of this writing).
When you then try to set the month to November, what's it to do? November only has 30 days... so it wraps it round to December.
If you change the order so that you set the day-of-month before the month, it works:
var date1 = new Date();
date1.setFullYear(2012); // year (four digits)
date1.setDate(1); // day of the month (from 1-31)
date1.setMonth(10); // month (from 0-11)
Or as implied by jbabey's answer:
var date1 = new Date();
date1.setFullYear(2012); // year (four digits)
date1.setMonth(10, 1); // month (from 0-11) and day (1-31)
The documentation isn't terribly clear, but it's at least suggestive:
If a parameter you specify is outside of the expected range, setMonth attempts to update the date information in the Date object accordingly. For example, if you use 15 for monthValue, the year will be incremented by 1 (year + 1), and 3 will be used for month.
("Accordingly" is far from precise, but it means the implementation is at least arguably correct...)

setMonth accepts a second parameter:
If you do not specify the dayValue parameter, the value returned from the getDate method is used.
When you set the month to 10 (November), it grabs the current day value (31) and sets that as the day. Since there are only 30 days in November, it rolls you over to December 1st.

You're creating a var containing the current date (new Date()) and then you're changing some of it's keys (year, month and day).
On the other hand new Date(2012, 10, 1, 0, 0, 0, 0) means "create a date object with those exact values".
And that's why your date objects aren't equal.

Calculate last day of month

If you provide 0 as the dayValue in Date.setFullYear you get the last day of the previous month:
d = new Date(); d.setFullYear(2008, 11, 0); // Sun Nov 30 2008
There is reference to this behaviour at mozilla. Is this a reliable cross-browser feature or should I look at alternative methods?

var month = 0; // January
var d = new Date(2008, month + 1, 0);
console.log(d.toString()); // last day in January
IE 6: Thu Jan 31 00:00:00 CST 2008
IE 7: Thu Jan 31 00:00:00 CST 2008
IE 8: Beta 2: Thu Jan 31 00:00:00 CST 2008
Opera 8.54: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.27: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.60: Thu Jan 31 2008 00:00:00 GMT-0600
Firefox 2.0.0.17: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Firefox 3.0.3: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Google Chrome 0.2.149.30: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Safari for Windows 3.1.2: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Output differences are due to differences in the toString() implementation, not because the dates are different.
Of course, just because the browsers identified above use 0 as the last day of the previous month does not mean they will continue to do so, or that browsers not listed will do so, but it lends credibility to the belief that it should work the same way in every browser.

I find this to be the best solution for me. Let the Date object calculate it for you.
var today = new Date();
var lastDayOfMonth = new Date(today.getFullYear(), today.getMonth()+1, 0);
Setting day parameter to 0 means one day less than first day of the month which is last day of the previous month.

I would use an intermediate date with the first day of the next month, and return the date from the previous day:
int_d = new Date(2008, 11+1,1);
d = new Date(int_d - 1);

In computer terms, new Date() and regular expression solutions are slow! If you want a super-fast (and super-cryptic) one-liner, try this one (assuming m is in Jan=1 format). I keep trying different code changes to get the best performance.
My current fastest version:
After looking at this related question Leap year check using bitwise operators (amazing speed) and discovering what the 25 & 15 magic number represented, I have come up with this optimized hybrid of answers (note the parameters m & y must obviously be integers for this to work):
function getDaysInMonth(m, y) {
return m===2 ? y & 3 || !(y%25) && y & 15 ? 28 : 29 : 30 + (m+(m>>3)&1);
}
Given the bit-shifting this obviously assumes that your m & y parameters are both integers, as passing numbers as strings would result in weird results.
JSFiddle: http://jsfiddle.net/TrueBlueAussie/H89X3/22/
JSPerf results: http://jsperf.com/days-in-month-head-to-head/5
For some reason, (m+(m>>3)&1) is more efficient than (5546>>m&1) on almost all browsers.
The only real competition for speed is from #GitaarLab, so I have created a head-to-head JSPerf for us to test on: http://jsperf.com/days-in-month-head-to-head/5
It works based on my leap year answer here: javascript to find leap year this answer here Leap year check using bitwise operators (amazing speed) as well as the following binary logic.
A quick lesson in binary months:
If you interpret the index of the desired months (Jan = 1) in binary you will notice that months with 31 days either have bit 3 clear and bit 0 set, or bit 3 set and bit 0 clear.
Jan = 1 = 0001 : 31 days
Feb = 2 = 0010
Mar = 3 = 0011 : 31 days
Apr = 4 = 0100
May = 5 = 0101 : 31 days
Jun = 6 = 0110
Jul = 7 = 0111 : 31 days
Aug = 8 = 1000 : 31 days
Sep = 9 = 1001
Oct = 10 = 1010 : 31 days
Nov = 11 = 1011
Dec = 12 = 1100 : 31 days
That means you can shift the value 3 places with >> 3, XOR the bits with the original ^ m and see if the result is 1 or 0 in bit position 0 using & 1. Note: It turns out + is slightly faster than XOR (^) and (m >> 3) + m gives the same result in bit 0.
JSPerf results: http://jsperf.com/days-in-month-perf-test/6

My colleague stumbled upon the following which may be an easier solution
function daysInMonth(iMonth, iYear)
{
return 32 - new Date(iYear, iMonth, 32).getDate();
}
stolen from http://snippets.dzone.com/posts/show/2099

A slight modification to solution provided by lebreeze:
function daysInMonth(iMonth, iYear)
{
return new Date(iYear, iMonth, 0).getDate();
}

I recently had to do something similar, this is what I came up with:
/**
* Returns a date set to the begining of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function beginningOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1)
date.setHours(0);
date.setMinutes(0);
date.setSeconds(0);
return date;
}
/**
* Returns a date set to the end of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function endOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1); // Avoids edge cases on the 31st day of some months
date.setMonth(date.getMonth() +1);
date.setDate(0);
date.setHours(23);
date.setMinutes(59);
date.setSeconds(59);
return date;
}
Pass it in a date, and it will return a date set to either the beginning of the month, or the end of the month.
The begninngOfMonth function is fairly self-explanatory, but what's going in in the endOfMonth function is that I'm incrementing the month to the next month, and then using setDate(0) to roll back the day to the last day of the previous month which is a part of the setDate spec:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/setDate
https://www.w3schools.com/jsref/jsref_setdate.asp
I then set the hour/minutes/seconds to the end of the day, so that if you're using some kind of API that is expecting a date range you'll be able to capture the entirety of that last day. That part might go beyond what the original post is asking for but it could help someone else looking for a similar solution.
Edit: You can also go the extra mile and set milliseconds with setMilliseconds() if you want to be extra precise.

How NOT to do it
Beware of any answers for the last of the month that look like this:
var last = new Date(date)
last.setMonth(last.getMonth() + 1) // This is the wrong way to do it.
last.setDate(0)
This works for most dates, but fails if date is already the last day of the month, on a month that has more days than the following month.
Example:
Suppose date is 07/31/21.
Then last.setMonth(last.getMonth() + 1) increments the month, but keeps the day set at 31.
You get a Date object for 08/31/21,
which is actually 09/01/21.
So then last.setDate(0) results in 08/31/21 when what we really wanted was 07/31/21.

try this one.
lastDateofTheMonth = new Date(year, month, 0)
example:
new Date(2012, 8, 0)
output:
Date {Fri Aug 31 2012 00:00:00 GMT+0900 (Tokyo Standard Time)}

This works for me.
Will provide last day of given year and month:
var d = new Date(2012,02,0);
var n = d.getDate();
alert(n);

This one works nicely:
Date.prototype.setToLastDateInMonth = function () {
this.setDate(1);
this.setMonth(this.getMonth() + 1);
this.setDate(this.getDate() - 1);
return this;
}

You can get the First and Last Date in the current month by following the code:
var dateNow = new Date();
var firstDate = new Date(dateNow.getFullYear(), dateNow.getMonth(), 1);
var lastDate = new Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0);
or if you want to format the date in your custom format then you can use moment js
var dateNow= new Date();
var firstDate=moment(new Date(dateNow.getFullYear(),dateNow.getMonth(), 1)).format("DD-MM-YYYY");
var currentDate = moment(new Date()).format("DD-MM-YYYY"); //to get the current date var lastDate = moment(new
Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0)).format("DD-MM-YYYY"); //month last date

This will give you current month first and last day.
If you need to change 'year' remove d.getFullYear() and set your year.
If you need to change 'month' remove d.getMonth() and set your year.
var d = new Date();
var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
var fistDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth(), 1).getDay())];
var LastDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth() + 1, 0).getDay())];
console.log("First Day :" + fistDayOfMonth);
console.log("Last Day:" + LastDayOfMonth);
alert("First Day :" + fistDayOfMonth);
alert("Last Day:" + LastDayOfMonth);

Try this:
function _getEndOfMonth(time_stamp) {
let time = new Date(time_stamp * 1000);
let month = time.getMonth() + 1;
let year = time.getFullYear();
let day = time.getDate();
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
day = 31;
break;
case 4:
case 6:
case 9:
case 11:
day = 30;
break;
case 2:
if (_leapyear(year))
day = 29;
else
day = 28;
break
}
let m = moment(`${year}-${month}-${day}`, 'YYYY-MM-DD')
return m.unix() + constants.DAY - 1;
}
function _leapyear(year) {
return (year % 100 === 0) ? (year % 400 === 0) : (year % 4 === 0);
}

const today = new Date();
let beginDate = new Date();
let endDate = new Date();
// fist date of montg
beginDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 1}-01 00:00:00`
);
// end date of month
// set next Month first Date
endDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 2}-01 :23:59:59`
);
// deducting 1 day
endDate.setDate(0);

Below function gives the last day of the month :
function getLstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 0).getDate()
}
console.log(getLstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 29
console.log(getLstDayOfMonFnc(new Date(2017, 2, 15))) // Output : 28
console.log(getLstDayOfMonFnc(new Date(2017, 11, 15))) // Output : 30
console.log(getLstDayOfMonFnc(new Date(2017, 12, 15))) // Output : 31
Similarly we can get first day of the month :
function getFstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 1).getDate()
}
console.log(getFstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 1

Here is an answer that conserves GMT and time of the initial date
var date = new Date();
var first_date = new Date(date); //Make a copy of the date we want the first and last days from
first_date.setUTCDate(1); //Set the day as the first of the month
var last_date = new Date(first_date); //Make a copy of the calculated first day
last_date.setUTCMonth(last_date.getUTCMonth() + 1); //Add a month
last_date.setUTCDate(0); //Set the date to 0, this goes to the last day of the previous month
console.log(first_date.toJSON().substring(0, 10), last_date.toJSON().substring(0, 10)); //Log the dates with the format yyyy-mm-dd

function getLastDay(y, m) {
return 30 + (m <= 7 ? ((m % 2) ? 1 : 0) : (!(m % 2) ? 1 : 0)) - (m == 2) - (m == 2 && y % 4 != 0 || !(y % 100 == 0 && y % 400 == 0));
}

set month you need to date and then set the day to zero ,so month begin in 1 - 31 in date function then get the last day^^
var last = new Date(new Date(new Date().setMonth(7)).setDate(0)).getDate();
console.log(last);

I know it's just a matter of semantics, but I ended up using it in this form.
var lastDay = new Date(new Date(2008, 11+1,1) - 1).getDate();
console.log(lastDay);
Since functions are resolved from the inside argument, outward, it works the same.
You can then just replace the year, and month / year with the required details, whether it be from the current date. Or a particular month / year.

If you need exact end of the month in miliseconds (for example in a timestamp):
d = new Date()
console.log(d.toString())
d.setDate(1)
d.setHours(23, 59, 59, 999)
d.setMonth(d.getMonth() + 1)
d.setDate(d.getDate() - 1)
console.log(d.toString())

The accepted answer doesn't work for me, I did it as below.
$( function() {
$( "#datepicker" ).datepicker();
$('#getLastDateOfMon').on('click', function(){
var date = $('#datepicker').val();
// Format 'mm/dd/yy' eg: 12/31/2018
var parts = date.split("/");
var lastDateOfMonth = new Date();
lastDateOfMonth.setFullYear(parts[2]);
lastDateOfMonth.setMonth(parts[0]);
lastDateOfMonth.setDate(0);
alert(lastDateOfMonth.toLocaleDateString());
});
});
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<link rel="stylesheet" href="/resources/demos/style.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
</head>
<body>
<p>Date: <input type="text" id="datepicker"></p>
<button id="getLastDateOfMon">Get Last Date of Month </button>
</body>
</html>

This will give you last day of current month.
notes: on ios device include time.
#gshoanganh
var date = new Date();
console.log(new Date(date.getFullYear(), date.getMonth() + 1, 0, 23, 59, 59));

if you just need to get the last date of a month following worked out for me.
var d = new Date();
const year = d.getFullYear();
const month = d.getMonth();
const lastDay = new Date(year, month +1, 0).getDate();
console.log(lastDay);
try it out here https://www.w3resource.com/javascript-exercises/javascript-date-exercise-9.php

In my case, this code was useful
end_date = new Date(2018, 3, 1).toISOString().split('T')[0]
console.log(end_date)

Categories

Resources