Javascript date increase by a year and subtract a day - javascript

I have a date from a vuetify date picker. I take that date and I am trying to format it to MM/DD/YYYY however I need to first add a year to it then subtract one day. So January 1 2022 will become December 31 2022. My code is as follows:
formatDateNextYear(date) {
if (!date) return null
let a = new Date(date);
a.setDate(a.getDate() - 1)
a.setFullYear(a.getFullYear+1)
const [year, month, day] = a.split('-')
return `${month}/${day}/${year}`
}
My issue is this does not seem to add the year and is not formatted correctly.

You forgot to call getFullYear, and instead of trying to format it yourself, you can use toLocaleDateString and pass in the locale you want the format to be in:
function formatDateNextYear(date) {
if (!date) return null;
let a = new Date(date);
a.setDate(a.getDate() - 1);
a.setFullYear(a.getFullYear() + 1);
return a.toLocaleDateString("en-US");
}
console.log(formatDateNextYear(new Date("01/01/2022")));

Related

How to convert utc time to local time on frontend [duplicate]

From the server I get a datetime variable in this format: 6/29/2011 4:52:48 PM and it is in UTC time. I want to convert it to the current user’s browser time zone using JavaScript.
How this can be done using JavaScript or jQuery?
Append 'UTC' to the string before converting it to a date in javascript:
var date = new Date('6/29/2011 4:52:48 PM UTC');
date.toString() // "Wed Jun 29 2011 09:52:48 GMT-0700 (PDT)"
In my point of view servers should always in the general case return a datetime in the standardized ISO 8601-format.
More info here:
http://www.w3.org/TR/NOTE-datetime
https://en.wikipedia.org/wiki/ISO_8601
IN this case the server would return '2011-06-29T16:52:48.000Z' which would feed directly into the JS Date object.
var utcDate = '2011-06-29T16:52:48.000Z'; // ISO-8601 formatted date returned from server
var localDate = new Date(utcDate);
The localDate will be in the right local time which in my case would be two hours later (DK time).
You really don't have to do all this parsing which just complicates stuff, as long as you are consistent with what format to expect from the server.
This is an universal solution:
function convertUTCDateToLocalDate(date) {
var newDate = new Date(date.getTime()+date.getTimezoneOffset()*60*1000);
var offset = date.getTimezoneOffset() / 60;
var hours = date.getHours();
newDate.setHours(hours - offset);
return newDate;
}
Usage:
var date = convertUTCDateToLocalDate(new Date(date_string_you_received));
Display the date based on the client local setting:
date.toLocaleString();
For me above solutions didn't work.
With IE the UTC date-time conversion to local is little tricky.
For me, the date-time from web API is '2018-02-15T05:37:26.007' and I wanted to convert as per local timezone so I used below code in JavaScript.
var createdDateTime = new Date('2018-02-15T05:37:26.007' + 'Z');
You should get the (UTC) offset (in minutes) of the client:
var offset = new Date().getTimezoneOffset();
And then do the correspondent adding or substraction to the time you get from the server.
Hope this helps.
This works for me:
function convertUTCDateToLocalDate(date) {
var newDate = new Date(date.getTime() - date.getTimezoneOffset()*60*1000);
return newDate;
}
Put this function in your head:
<script type="text/javascript">
function localize(t)
{
var d=new Date(t+" UTC");
document.write(d.toString());
}
</script>
Then generate the following for each date in the body of your page:
<script type="text/javascript">localize("6/29/2011 4:52:48 PM");</script>
To remove the GMT and time zone, change the following line:
document.write(d.toString().replace(/GMT.*/g,""));
This is a simplified solution based on Adorjan Princ´s answer:
function convertUTCDateToLocalDate(date) {
var newDate = new Date(date);
newDate.setMinutes(date.getMinutes() - date.getTimezoneOffset());
return newDate;
}
or simpler (though it mutates the original date):
function convertUTCDateToLocalDate(date) {
date.setMinutes(date.getMinutes() - date.getTimezoneOffset());
return date;
}
Usage:
var date = convertUTCDateToLocalDate(new Date(date_string_you_received));
After trying a few others posted here without good results, this seemed to work for me:
convertUTCDateToLocalDate: function (date) {
return new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate(), date.getHours(), date.getMinutes(), date.getSeconds()));
}
And this works to go the opposite way, from Local Date to UTC:
convertLocalDatetoUTCDate: function(date){
return new Date(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate(), date.getUTCHours(), date.getUTCMinutes(), date.getUTCSeconds());
}
Add the time zone at the end, in this case 'UTC':
theDate = new Date( Date.parse('6/29/2011 4:52:48 PM UTC'));
after that, use toLocale()* function families to display the date in the correct locale
theDate.toLocaleString(); // "6/29/2011, 9:52:48 AM"
theDate.toLocaleTimeString(); // "9:52:48 AM"
theDate.toLocaleDateString(); // "6/29/2011"
if you have
"2021-12-28T18:00:45.959Z" format
you can use this in js :
// myDateTime is 2021-12-28T18:00:45.959Z
myDate = new Date(myDateTime).toLocaleDateString('en-US');
// myDate is 12/28/2021
myTime = new Date(myDateTime).toLocaleTimeString('en-US');
// myTime is 9:30:45 PM
you just have to put your area string instead of "en-US" (e.g. "fa-IR").
also you can use options for toLocaleTimeString like { hour: '2-digit', minute: '2-digit' }
myTime = new Date(myDateTime).toLocaleTimeString('en-US',{ hour: '2-digit', minute: '2-digit' });
// myTime is 09:30 PM
more information for toLocaleTimeString and toLocaleDateString
Use this for UTC and Local time convert and vice versa.
//Covert datetime by GMT offset
//If toUTC is true then return UTC time other wise return local time
function convertLocalDateToUTCDate(date, toUTC) {
date = new Date(date);
//Local time converted to UTC
console.log("Time: " + date);
var localOffset = date.getTimezoneOffset() * 60000;
var localTime = date.getTime();
if (toUTC) {
date = localTime + localOffset;
} else {
date = localTime - localOffset;
}
date = new Date(date);
console.log("Converted time: " + date);
return date;
}
Matt's answer is missing the fact that the daylight savings time could be different between Date() and the date time it needs to convert - here is my solution:
function ConvertUTCTimeToLocalTime(UTCDateString)
{
var convertdLocalTime = new Date(UTCDateString);
var hourOffset = convertdLocalTime.getTimezoneOffset() / 60;
convertdLocalTime.setHours( convertdLocalTime.getHours() + hourOffset );
return convertdLocalTime;
}
And the results in the debugger:
UTCDateString: "2014-02-26T00:00:00"
convertdLocalTime: Wed Feb 26 2014 00:00:00 GMT-0800 (Pacific Standard Time)
In case you don't mind usingmoment.js and your time is in UTC just use the following:
moment.utc('6/29/2011 4:52:48 PM').toDate();
if your time is not in utc but any other locale known to you, then use following:
moment('6/29/2011 4:52:48 PM', 'MM-DD-YYYY', 'fr').toDate();
if your time is already in local, then use following:
moment('6/29/2011 4:52:48 PM', 'MM-DD-YYYY');
To me the simplest seemed using
datetime.setUTCHours(datetime.getHours());
datetime.setUTCMinutes(datetime.getMinutes());
(i thought the first line could be enough but there are timezones which are off in fractions of hours)
This is what I'm doing to convert UTC to my Local Time:
const dataDate = '2020-09-15 07:08:08'
const utcDate = new Date(dataDate);
const myLocalDate = new Date(Date.UTC(
utcDate.getFullYear(),
utcDate.getMonth(),
utcDate.getDate(),
utcDate.getHours(),
utcDate.getMinutes()
));
document.getElementById("dataDate").innerHTML = dataDate;
document.getElementById("myLocalDate").innerHTML = myLocalDate;
<p>UTC<p>
<p id="dataDate"></p>
<p>Local(GMT +7)<p>
<p id="myLocalDate"></p>
Result: Tue Sep 15 2020 14:08:00 GMT+0700 (Indochina Time).
Using YYYY-MM-DD hh:mm:ss format :
var date = new Date('2011-06-29T16:52:48+00:00');
date.toString() // "Wed Jun 29 2011 09:52:48 GMT-0700 (PDT)"
For converting from the YYYY-MM-DD hh:mm:ss format, make sure your date follow the ISO 8601 format.
Year:
YYYY (eg 1997)
Year and month:
YYYY-MM (eg 1997-07)
Complete date:
YYYY-MM-DD (eg 1997-07-16)
Complete date plus hours and minutes:
YYYY-MM-DDThh:mmTZD (eg 1997-07-16T19:20+01:00)
Complete date plus hours, minutes and seconds:
YYYY-MM-DDThh:mm:ssTZD (eg 1997-07-16T19:20:30+01:00)
Complete date plus hours, minutes, seconds and a decimal fraction of a second
YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00) where:
YYYY = four-digit year
MM = two-digit month (01=January, etc.)
DD = two-digit day of month (01 through 31)
hh = two digits of hour (00 through 23) (am/pm NOT allowed)
mm = two digits of minute (00 through 59)
ss = two digits of second (00 through 59)
s = one or more digits representing a decimal fraction of a second
TZD = time zone designator (Z or +hh:mm or -hh:mm)
Important things to note
You must separate the date and the time by a T, a space will not work in some browsers
You must set the timezone using this format +hh:mm, using a string for a timezone (ex. : 'UTC') will not work in many browsers. +hh:mm represent the offset from the UTC timezone.
A JSON date string (serialized in C#) looks like "2015-10-13T18:58:17".
In angular, (following Hulvej) make a localdate filter:
myFilters.filter('localdate', function () {
return function(input) {
var date = new Date(input + '.000Z');
return date;
};
})
Then, display local time like:
{{order.createDate | localdate | date : 'MMM d, y h:mm a' }}
For me, this works well
if (typeof date === "number") {
time = new Date(date).toLocaleString();
} else if (typeof date === "string"){
time = new Date(`${date} UTC`).toLocaleString();
}
I Answering This If Any one want function that display converted time to specific id element and apply date format string yyyy-mm-dd
here date1 is string and ids is id of element that time going to display.
function convertUTCDateToLocalDate(date1, ids)
{
var newDate = new Date();
var ary = date1.split(" ");
var ary2 = ary[0].split("-");
var ary1 = ary[1].split(":");
var month_short = Array('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec');
newDate.setUTCHours(parseInt(ary1[0]));
newDate.setUTCMinutes(ary1[1]);
newDate.setUTCSeconds(ary1[2]);
newDate.setUTCFullYear(ary2[0]);
newDate.setUTCMonth(ary2[1]);
newDate.setUTCDate(ary2[2]);
ids = document.getElementById(ids);
ids.innerHTML = " " + newDate.getDate() + "-" + month_short[newDate.getMonth() - 1] + "-" + newDate.getFullYear() + " " + newDate.getHours() + ":" + newDate.getMinutes() + ":" + newDate.getSeconds();
}
i know that answer has been already accepted but i get here cause of google and i did solve with getting inspiration from accepted answer so i did want to just share it if someone need.
#Adorojan's answer is almost correct. But addition of offset is not correct since offset value will be negative if browser date is ahead of GMT and vice versa.
Below is the solution which I came with and is working perfectly fine for me:
// Input time in UTC
var inputInUtc = "6/29/2011 4:52:48";
var dateInUtc = new Date(Date.parse(inputInUtc+" UTC"));
//Print date in UTC time
document.write("Date in UTC : " + dateInUtc.toISOString()+"<br>");
var dateInLocalTz = convertUtcToLocalTz(dateInUtc);
//Print date in local time
document.write("Date in Local : " + dateInLocalTz.toISOString());
function convertUtcToLocalTz(dateInUtc) {
//Convert to local timezone
return new Date(dateInUtc.getTime() - dateInUtc.getTimezoneOffset()*60*1000);
}
Based on #digitalbath answer, here is a small function to grab the UTC timestamp and display the local time in a given DOM element (using jQuery for this last part):
https://jsfiddle.net/moriz/6ktb4sv8/1/
<div id="eventTimestamp" class="timeStamp">
</div>
<script type="text/javascript">
// Convert UTC timestamp to local time and display in specified DOM element
function convertAndDisplayUTCtime(date,hour,minutes,elementID) {
var eventDate = new Date(''+date+' '+hour+':'+minutes+':00 UTC');
eventDate.toString();
$('#'+elementID).html(eventDate);
}
convertAndDisplayUTCtime('06/03/2015',16,32,'eventTimestamp');
</script>
You can use momentjs ,moment(date).format() will always give result in local date.
Bonus , you can format in any way you want. For eg.
moment().format('MMMM Do YYYY, h:mm:ss a'); // September 14th 2018, 12:51:03 pm
moment().format('dddd'); // Friday
moment().format("MMM Do YY");
For more details you can refer Moment js website
this worked well for me with safari/chrome/firefox :
const localDate = new Date(`${utcDate.replace(/-/g, '/')} UTC`);
I believe this is the best solution:
let date = new Date(objDate);
date.setMinutes(date.getTimezoneOffset());
This will update your date by the offset appropriately since it is presented in minutes.
tl;dr (new Date('6/29/2011 4:52:48 PM UTC')).toString()
The source string must specify a time zone or UTC.
One-liner:
(new Date('6/29/2011 4:52:48 PM UTC')).toString()
Result in one of my web browsers:
"Wed Jun 29 2011 09:52:48 GMT-0700 (Pacific Daylight Time)"
This approach even selects standard/daylight time appropriately.
(new Date('1/29/2011 4:52:48 PM UTC')).toString()
Result in my browser:
"Sat Jan 29 2011 08:52:48 GMT-0800 (Pacific Standard Time)"
using dayjs library:
(new Date()).toISOString(); // returns 2021-03-26T09:58:57.156Z (GMT time)
dayjs().format('YYYY-MM-DD HH:mm:ss,SSS'); // returns 2021-03-26 10:58:57,156 (local time)
(in nodejs, you must do before using it: const dayjs = require('dayjs');
in other environtments, read dayjs documentation.)
This works on my side
Option 1: If date format is something like "yyyy-mm-dd" or "yyyy-mm-dd H:n:s", ex: "2021-12-16 06:07:40"
With this format It doesnt really know if its a local format or a UTC time. So since we know that the date is a UTC we have to make sure that JS will know that its a UTC. So we have to set the date as UTC.
function setDateAsUTC(d) {
let date = new Date(d);
return new Date(
Date.UTC(
date.getFullYear(),
date.getMonth(),
date.getDate(),
date.getHours(),
date.getMinutes(),
date.getSeconds()
)
);
}
and then use it
let d = "2021-12-16 06:07:40";
setDateAsUTC(d).toLocaleString();
// output: 12/16/2021, 6:07:40 AM
Options 2: If UTC date format is ISO-8601. Mostly servers timestampz format are in ISO-8601 ex: '2011-06-29T16:52:48.000Z'. With this we can just pass it to the date function and toLocaleString() function.
let newDate = "2011-06-29T16:52:48.000Z"
new Date(newDate).toLocaleString();
//output: 6/29/2011, 4:52:48 PM
In JavaScript I used:
var updaated_time= "2022-10-25T06:47:42.000Z"
{{updaated_time | date: 'dd-MM-yyyy HH:mm'}} //output: 26-10-2022 12:00
I wrote a nice little script that takes a UTC epoch and converts it the client system timezone and returns it in d/m/Y H:i:s (like the PHP date function) format:
getTimezoneDate = function ( e ) {
function p(s) { return (s < 10) ? '0' + s : s; }
var t = new Date(0);
t.setUTCSeconds(e);
var d = p(t.getDate()),
m = p(t.getMonth()+1),
Y = p(t.getFullYear()),
H = p(t.getHours()),
i = p(t.getMinutes()),
s = p(t.getSeconds());
d = [d, m, Y].join('/') + ' ' + [H, i, s].join(':');
return d;
};

How to use the Time period in date time

I have a form that sends the value of year and months from an input and then while sending the value to the server I am converting that values to ISO string like that:
const toIsoString = (year, month, day) => moment(new Date(year, month - 1, day)).toISOString(true).split('.')[0];
And then in the values I am using it like this.
StartDate: toIsoString(data.StartYear, parseInt(data.StartMonth, 10), 1),
In that case It is sending the value like this:
startDate: "2021-01-01T00:00:00"
Does anybody know why the Time period is being ignored and how can I also send the time period with the year, month and date values.Any helps would be highly appreciated.Thanks...
Does anybody know why the Time period is being ignored and how can I also send the time period with the year, month and date values.Any helps would be highly appreciated.
The time isn't ignored. In the function:
const toIsoString = (year, month, day) =>
moment(new Date(year, month - 1, day)).toISOString(true).split('.')[0];
the values for hour, minute, second and millisecond are omitted so they default to 0. What time are you expecting?
If you want the current local time added to the date, then create a date and set the year, month and day to the required values without modifying the time (though I don't know why you'd want to do that).
Rather than creating a string that you then need to further process, tell moment.js the format you want:
function toIsoString (year, month, day) {
return moment(new Date().setFullYear(year, month-1, day)).format('YYYY-MM-DD HH:mm:ss');
}
console.log(toIsoString('2021','1','1'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.26.0/moment.min.js"></script>
You can also do that without a library, see How to format a JavaScript date, e.g.:
function formatDate(year, month, date) {
let z = n => (n<10?'0':'') + Number(n);
return `${year}-${z(month)}-${z(date)} ${
new Date().toLocaleString('en',{
hour12:false,
hour:'2-digit',
minute:'2-digit',
second:'2-digit'})
}`;
}
console.log(formatDate('2021','1','01'))
Its because you are only setting year, month and date while creating moment object. You are not setting time
You should do something like
const toIsoString = (year, month, day) => {
const currDate = moment(new Date());
currDate.year(year);
currDate.month(month - 1);
currDate.date(day);
return currDate.toISOString(true).split('.')[0];
}
Or simply use set function
const toIsoString = (year, month, day) => {
const currDate = moment(new Date());
currDate.set({
'year': year,
'month': (month - 1),
'date': day
});
return currDate.toISOString(true).split('.')[0];
}

How to get the date of last day of week with a specific timezone using js

I want to get date of the last day of week with a specific timezone.
I got this code that works good but it shows the computer timezone. i want to add a specific timezone like GMT-0500
{
var lastday = date.getDate() - (date.getDay() - 1) + 6;
return new Date(date.setDate(lastday));
}
dt = new Date();
dt.setHours(23,59,59,999);
document.getElementById("lastday").innerHTML = endOfWeek(dt).toString();
console.log(endOfWeek(dt).toString());
How can i change the timezone? please help.

What is the source of this off-by-one error in a JavaScript date?

I am trying to write a function that will take a string like 07/2020 and then return whether it is more than three months away.
I have written a function isMoreThan3MonthsHence that I am reasonably sure works correctly:
const isMoreThan3MonthsHence = ({ utcYear, utcMonth },
now = new Date,
target = new Date(Date.UTC(utcYear, utcMonth)),
threeMonthsAway = new Date(now.valueOf()).setUTCMonth(now.getUTCMonth() + 3)) =>
(target > threeMonthsAway)
console.log(isMoreThan3MonthsHence({ utcYear: 2020, utcMonth: 7 })) // true (correct!)
The problem comes when I try to construct a Date object to use to populate the arguments for isMoreThan3MonthsHence.
const validate = (str,
[localMonth, localYear] = str.split('/'),
date = new Date(+localYear, (+localMonth)-1)) =>
isMoreThan3MonthsHence({ utcYear: date.getUTCFullYear(), utcMonth: date.getUTCMonth() })
// Note: input is one-based months
console.log(validate('07/2020')) // false (but should be true!)
I think the reason is that new-ing up a Date in validate without specifying the timezone will use the local timezone in effect at the supplied date, which will be BST (UTC+1).
Wed Jul 01 2020 00:00:00 GMT+0100 (British Summer Time)
This time is actually 2300hrs on June 30th in UTC. So the month is actually 5 in zero-based terms. But I don't want this behavior. I want it so specifying July actually means July in UTC.
How can I fix this?
It looks like you're mixing the usage of Date.UTC and not when instantiating dates. For example, if you use the following for your validate function:
const validate = (str,
[month, year] = str.split('/'),
date = new Date(Date.UTC(+year, (+month)-1))) =>
isMoreThan3MonthsHence({ utcYear: date.getUTCFullYear(), utcMonth: date.getUTCMonth() })
// Note: input is one-based months
console.log(validate('07/2020')) // Now true
It works as expected: JSFiddle
Removing the usage of Date.UTC altogether would perform the calculation in the user's local timezone, with any applicable daylight saving adjustment included. This could be seen as a valid approach, however would result in the behaviour you have described.
Note I've renamed the local prefixed variables based on feedback from Bergi. Using Date.UTC implies you're passing in UTC arguments.
Other than mixing UTC and local dates, the way you're adding 3 months will cause an incorrect response for dates like 31 March, where adding 3 months simply by incrementing the month number results in a date for 1 July. See Adding months to a Date in JavaScript.
So validate('07,2020') will return false if run on 31 March.
To fix that, when adding months, check that the updated date is still on the same day in the month, otherwise it's rolled over so set it to the last day of the previous month.
function validate(s) {
let testDate = addMonths(new Date(), 3);
let [m, y] = s.split(/\D/);
return testDate < new Date(y, m-1);
};
function addMonths(date, months) {
let d = date.getDate();
date.setMonth(date.getMonth() + +months);
// If rolled over to next month, set to last day of previous month
if (date.getDate() != d) {
date.setDate(0);
}
return date;
}
// Sample
console.log('On ' + new Date().toDateString() + ':');
['07/2020', '04/2020'].forEach(
s => console.log(s + ' - ' + validate(s))
);

Get a date object (six months prior) from another date object

How can I create a date object which is less than n number of months from another date object? I am looking for something like DateAdd().
Example:
var objCurrentDate = new Date();
Now using objCurrentDate, how can I create a Date object having a date which is six months older than today's date / objCurrentDate?
You can implement very easily an "addMonths" function:
function addMonths(date, months) {
date.setMonth(date.getMonth() + months);
return date;
}
addMonths(new Date(), -6); // six months before now
// Thu Apr 30 2009 01:22:46 GMT-0600
addMonths(new Date(), -12); // a year before now
// Thu Oct 30 2008 01:20:22 GMT-0600
EDIT: As reported by #Brien, there were several problems with the above approach. It wasn't handling correctly the dates where, for example, the original day in the input date is higher than the number of days in the target month.
Another thing I disliked is that the function was mutating the input Date object.
Here's a better implementation handling the edge cases of the end of months and this one doesn't cause any side-effects in the input date supplied:
const getDaysInMonth = (year, month) => new Date(year, month, 0).getDate()
const addMonths = (input, months) => {
const date = new Date(input)
date.setDate(1)
date.setMonth(date.getMonth() + months)
date.setDate(Math.min(input.getDate(), getDaysInMonth(date.getFullYear(), date.getMonth()+1)))
return date
}
console.log(addMonths(new Date('2020-01-31T00:00:00'), -6))
// "2019-07-31T06:00:00.000Z"
console.log(addMonths(new Date('2020-01-31T00:00:00'), 1))
// "2020-02-29T06:00:00.000Z"
console.log(addMonths(new Date('2020-05-31T00:00:00'), -6))
// "2019-11-30T06:00:00.000Z"
console.log(addMonths(new Date('2020-02-29T00:00:00'), -12))
// "2019-02-28T06:00:00.000Z"
Create date object and pass the value of n, where n is number(add/sub) of month.
var dateObj = new Date();
var requiredDate= dateObj.setMonth(dateObj.getMonth() - n);
var oldDate:Date = new Date();
/*
Check and adjust the date -
At the least, make sure that the getDate() returns a
valid date for the calculated month and year.
If it's not valid, change the date as per your needs.
You might want to reset it to 1st day of the month/last day of the month
or change the month and set it to 1st day of next month or whatever.
*/
if(oldDate.getMonth() < n)
oldDate.setFullYear(oldDate.getFullYear() - 1);
oldDate.setMonth((oldDate.getMonth() + n) % 12);
You have to be careful because dates have a lot of edge cases. For example, merely changing the month back by 6 doesn't account for the differing number of days in each month. For example, if you run a function like:
function addMonths(date, months) {
date.setMonth((date.getMonth() + months) % 12);
return date;
}
addMonths(new Date(2020, 7, 31), -6); //months are 0 based so 7 = August
The resulting date to return would be February 31st, 2020. You need to account for differences in the number of days in a month. Other answers have suggested this in various ways, by moving it to the first of the month, or the last of the month, or the first of the next month, etc. Another way to handle it is to keep the date if it is valid, or to move it to the end of the month if it overflows the month's regular dates. You could write this like:
function addMonths(date, months) {
var month = (date.getMonth() + months) % 12;
//create a new Date object that gets the last day of the desired month
var last = new Date(date.getFullYear(), month + 1, 0);
//compare dates and set appropriately
if (date.getDate() <= last.getDate()) {
date.setMonth(month);
}
else {
date.setMonth(month, last.getDate());
}
return date;
}
This at least ensures that the selected day won't "overflow" the month that it is being moved to. Finding the last day of the month with the datePart = 0 method is documented here.
This function still leaves a lot to be desired, as it doesn't add years and you can't subtract more than a year (or you will run into a new issue with negatives being involved). However, fixing those and the other issues you may run into (namely timezones) will be left as an exercise for the reader.

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