I have the following snippet of code (actually I am using new Date() to get today (4th March 2016), but it won't be March for ever, so to be a sensible test I had made the date explicitly.
var n = new Date(2016,2,4);
var d = new Date (
n.getFullYear(),
n.getMonth(),
-1,
6,0,0);
console.log(d.toString());
when n is now (except it isn't) and d is a new date which I want to be the last day of the preceding month. I am NOT getting 29th February 2016 6:00am UTC, which is what I would have expected, instead I am getting 28th February.
This gives the same result in both Chrome and Iceweasel (Firefox). How should I find the last day of the previous month (especially, like this year when it is a leap year)
If it matters, I am in the GMT timezone.
That's because days are 1 based, not 0 based.
var march4 = new Date(2016, 2, 4);
var feb29 = new Date(
march4.getFullYear(),
march4.getMonth(),
0); // <-- go to the day before the first of the given month
console.log(feb29); // Mon Feb 29 2016 00:00:00 GMT-0700 (Mountain Standard Time)
For reference, if you pull the same trick for April to March, you'll get March 31st.
var april = new Date(2016, 3, 4);
var march = new Date(
april.getFullYear(),
april.getMonth(),
0);
console.log(march); // Thu Mar 31 2016 06:00:00 GMT-0600 (Mountain Daylight Time)
In fact, it recognizes
If you try this, it works:
Date (2016, 2, 0);
It brings to me Mon Feb 29 2016 00:00:00 GMT-0300
Instead of -1, try 0:
var n = new Date(2016,2,1);
var d = new Date (
n.getFullYear(),
n.getMonth(),
0,
6,0,0);
console.log(d.toString());
Related
I have the following code using Google Apps Script, but when I log it out I get the following results. I want GAS to log the next month and stop once it gets to "lastDateofYear ". For whatever reason, the year doesn't change in my results, it just keeps repeating the current year. Please help.
var thisDate = "Mon Dec 20 00:00:00 GMT-06:00 2021";
var nextYear = Number(currentYear)+1;
var lastDateofYear = new Date("12-31-"+nextYear);
for(var i=thisDate; i <= lastDateofYear; ){
var currentiDate = new Date(i);
var month = currentiDate.getMonth()+1;
i.setMonth((month) % 12);
i.setDate(currentiDate.getDate());
Logger.log(currentiDate);
}
RESULTS:
Mon Dec 20 00:00:00 GMT-06:00 2021
Wed Jan 20 00:00:00 GMT-06:00 2021
Sat Feb 20 00:00:00 GMT-06:00 2021
Sat Mar 20 00:00:00 GMT-05:00 2021
Tue Apr 20 00:00:00 GMT-05:00 2021
Thu May 20 00:00:00 GMT-05:00 2021
Sun Jun 20 00:00:00 GMT-05:00 2021
Tue Jul 20 00:00:00 GMT-05:00 2021
Fri Aug 20 00:00:00 GMT-05:00 2021
Mon Sep 20 00:00:00 GMT-05:00 2021
Wed Oct 20 00:00:00 GMT-05:00 2021
Sat Nov 20 00:00:00 GMT-06:00 2021
Mon Dec 20 00:00:00 GMT-06:00 2021
Wed Jan 20 00:00:00 GMT-06:00 2021
Sat Feb 20 00:00:00 GMT-06:00 2021
Sat Mar 20 00:00:00 GMT-05:00 2021
Tue Apr 20 00:00:00 GMT-05:00 2021
As I understand it, you want to print each month from the given date to the last month of the next year of the given date in the log.
You can do this in the following code:
let start = new Date("Mon Dec 20 00:00:00 GMT-06:00 2021");
let currentYear = new Date().getFullYear();
let nextYear = currentYear + 1;
let end = new Date(nextYear, 11, 31);
while (start <= end) {
// You can use Logger.log() here if you want. I use console.log() for demo purpose
console.log(new Date(start).toDateString());
start.setMonth(start.getMonth() + 1);
}
If I got any part wrong, feel free to point it out to me in the comments.
There is a lot to say about your code:
var thisDate = "Mon Dec 20 00:00:00 GMT-06:00 2021";
That timestamp format is not supported by ECMA-262, so don't use the built–in parser to parse it, see Why does Date.parse give incorrect results?
var nextYear = Number(currentYear)+1;
Where does currentYear come from?
var lastDateofYear = new Date("12-31-"+nextYear);
Parsing of an unsupported format, see above. In Safari it returns an invalid date.
for(var i=thisDate; i <= lastDateofYear; ){
Sets i to the string value assigned to thisDate. Since lastDateOfYear is an invalid date in Safari and Firefox, so the test i <= NaN is never true and the loop is never entered.
var currentiDate = new Date(i);
Parses i, see above.
var month = currentiDate.getMonth()+1;
i.setMonth((month) % 12);
i is a string, which doesn't have a setMonth method so I'd expect a Type error like "i.setMonth is not a function" if the loop actually runs.
i.setDate(currentiDate.getDate());
Another Type error as above (but it won't get this far).
Logger.log(currentiDate);
}
It seems you want to sequentially add 1 month to a date until it reaches the same date in the following year. Trivially, you can just add 1 month until you get to the same date next year, something like:
let today = new Date();
let nextYear = new Date(today.getFullYear() + 1, today.getMonth(), today.getDate());
let result = [];
do {
result.push(today.toString());
today.setMonth(today.getMonth() + 1);
} while (today <= nextYear)
However, adding months is not that simple. If you add 1 month to 1 Jan, you'll get 2 or 3 Mar depending on whether it's a leap year or not. And adding 1 month to 31 Aug will return 1 Oct.
Many "add month" functions check to see if the date rolls over an extra month and if it does, set the date back to the end of the previous month by setting the date to 0, so 31 Jan + 1 month gives 28 or 29 Feb.
But if you cycle over a year using that algorithm, you'll get say 31 Jan, 28 Feb, 28 Mar, 28 Apr etc. rather than 31 Jan, 28 Feb, 31 Mar, 30 Apr, etc.
See JavaScript function to add X months to a date and How to add months to a date in JavaScript?
A more robust way is to have a function that adds n months to a date and increment the months to add rather than the date itself so the month–end problem can be dealt with separately for each addition, e.g.
/* Add n months to a date. If date rolls over an extra month,
* set to last day of previous month, e.g.
* 31 Jan + 1 month => 2 Mar, roll back => 28 Feb
*
* #param {number} n - months to add
* #param {Date} date - date to add months to, default today
* #returns {Date} new Date object, doesn't modify passed Date
*/
function addMonths(n, date = new Date()) {
let d = new Date(+date);
let day = d.getDate();
d.setMonth(d.getMonth() + n);
if (d.getDate() != day) d.setDate(0);
return d;
}
/* return array of n dates at 1 month intervals. List is
* inclusive so n + 1 Dates returned.
*
* #param {Date} start - start date
* #param {number} n - number of months to return
* #returns {Array} array of Dates
*/
function getMonthArray(n, start = new Date()) {
let result = [];
for (let i=0; i<n; i++) {
result.push(addMonths(i, start));
}
return result;
}
// Examples
// Start on 1 Dec
getMonthArray(12, new Date(2021,11,1)).forEach(
d => console.log(d.toDateString())
);
// Start on 31 Dec
getMonthArray(12, new Date(2021,11,31)).forEach(
d => console.log(d.toDateString())
);
The functions don't attempt to parse timestamps to Dates, that responsibility is left to the caller.
I have problem with boostrap- datepicker. The core of my problem in such example
var array = [2017, 12, 27];
var date = new Date(array);
console.log(date);
//Wed Dec 27 2017 00:00:00 GMT+0300 (RTZ 2 (winter))
var day = date.getUTCDate();
console.log(day);
//26 -> I WANT 27
console.log(month);
//11 -> I WANT 12
console.log(year);
//2017
As you can see at the end i get 26 (the day what i need is 27) and 11 (the month what i need is 12).
How can i change this code (remove my timezone) to get 27, 12, 2017
There are two problems you're running into:
The difference between your timezone (GMT+0300) and UTC means that midnight December 27th 2017 in your timezone is 9p.m. December 26th 2017 UTC.
I'm assuming you got month via getUTCMonth. Month values start with 0 = January, which is why you're getting 11.
To get midnight December 27th 2017 in a Date, use Date.UTC:
var dt = new Date(Date.UTC(2017, 12 - 1, 27));
console.log(dt.getUTCDate()); // 27
console.log(dt.getUTCMonth() + 1); // 12
console.log(dt.getUTCFullYear()); // 2017
Note the + 1 after getUTCMonth, since again, month numbers are 0 = January through 11 = December.
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)
The issue:
Different formats for new Date() in IE 10 - IE 11.
Javascript:
IE 11 / Chrome :
var m = new Date("2014-07-04T04:00:00");
console.log(m); // Fri Jul 04 2014 06:00:00 GMT+0200 (W. Europe Summer Time)
IE 10:
var m = new Date("2014-07-04T04:00:00");
console.log(m); // Fri Jul 4 04:00:00 UTC+0200 2014
Is possible to use one ring to rule them all?
You shouldn't pass a string to new Date, specifically for this reason.
Instead, you should either give it the individual arguments:
new Date(2014, 6, 4, 4, 0, 0); // remember months are zero-based
Or, if you want to give it a time in UTC, try:
var d = new Date();
d.setUTCFullYear(2014);
d.setUTCMonth(6);
d.setUTCDate(4);
d.setUTCHours(4);
d.setUTCMinutes(0);
d.setUTCSeconds(0);
d.setUTCMilliseconds(0);
You can, of course, make a function to do this.
Alternatively, if you have a timestamp, you can simply do:
var d = new Date();
d.setTime(1404446400000);
To complete the answer a bit. The UTC example given is dangerous, given that you execute on 31st of May (or any other 31st day of month) the following:
var d = new Date();
d.setUTCFullYear(2014);
d.setUTCMonth(5);
d.setUTCDate(4);
d.setUTCHours(4);
d.setUTCMinutes(0);
d.setUTCSeconds(0);
d.setUTCMilliseconds(0);
it will produce "2014 July 4 04:00:00".
So prefer Date.UTC function instead:
new Date(Date.UTC(2014, 5, 4, 4, 0, 0, 0))
it will produce "2014 June 4 04:00:00".
While trying to find out why I was having issues while working on a calendar, I ran into this issue. When setting the month to 8, the date is set to October, when the month is set to 9, the date is set to October.
Code to test
var d = new Date();
document.write(d.getMonth());
d.setMonth(8);
document.write(d.getMonth());
d.setMonth(9);
document.write(d.getMonth());
output:
799
The current date is August 31st 2012, the month number should be 7, since the javascript months are 0 based.
Can someone explain this? I have been able to reproduce it on more than one computer.
September only has 30 days - when you set the day to 31 (or create a date on the 31st of some month) and then change the month to one with fewer than 31 days JavaScript rolls the date over into the next month (in this case October). In other words, the date overflows.
> var d = new Date()
> d
Fri Aug 31 2012 22:53:50 GMT-0400 (EDT)
// Set the month to September, leaving the day set to the 31st
> d.setMonth(8)
> d
Mon Oct 01 2012 22:53:50 GMT-0400 (EDT)
// Doing the same thing, changing the day first
> var d = new Date()
> d
Fri Aug 31 2012 22:53:50 GMT-0400 (EDT)
> d.setDate(30)
> d
Thu Aug 30 2012 22:53:50 GMT-0400 (EDT)
> d.setMonth(8)
Sun Sep 30 2012 22:53:50 GMT-0400 (EDT)
So the simple answer is, because the date for today is the 31st of August and the 31st of September is October 1st.