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Get difference between 2 dates in JavaScript? [duplicate]
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Closed 4 years ago.
I tried so many solution on stack overflow itself, but not get the difference in js.
I was using
var days = ('13-10-2018'- '13-09-2018') / (1000 * 60 * 60 * 24)]
Well, there are 2 issues here.
First, you need to use your date strings to construct a proper JavaScript Date object, which only supports IETF-compliant RFC 2822 timestamps and also a version of ISO8601, as you can see in MDN. Therefore, you can't use DD-MM-YYYY, but you could use MM-DD-YYYY
Another way to construct a Date object is to use this syntax:
new Date(year, monthIndex [, day [, hours [, minutes [, seconds [, milliseconds]]]]]);
So, to calculate the difference between 2 dates in the format DD-MM-YYYY, you first need to parse that and create two Date objects. Then, you call Date.prototype.getTime() in both of them and calculate the absolute difference in milliseconds. Lastly, you convert that to days dividing by 3600000 * 24 and rounding (if you don't want decimal days):
function getDateFromDDMMYYYY(dateString) {
const [day, month, year] = dateString.split('/');
return new Date(
parseInt(year),
parseInt(month) - 1,
parseInt(day)
);
}
const diff = Math.abs(getDateFromDDMMYYYY('13/10/2018').getTime() - getDateFromDDMMYYYY('13/09/2018').getTime());
const days = Math.round(diff / (3600000 * 24));
console.log(`${ days } ${ days === 1 ? 'day' : 'days' }`);
The way you are trying to subtract dates ('13-10-2018'- '13-09-2018') is wrong. This will give an error NaN (Not a number) because '13-10-2018' for instance is a string and can't be automatically converted to a Date object. if you ask '100' - '20' this will give you 80 as javascript automatically parses a string that can be converted to integers or floats when arithmetic operators are applied but in your case, it's '13-10-2018' that can't be parsed either as an integer or float because parsing it won't give any number.
If the date is in string format then you can parse it in following way and then perform some operation, Since your date is in DD-MM-YYYY I suggest you change it either in MM-DD-YYYY or in YYYY-MM-DD, for more info about Date you can look up to the this link.
let timeDifference = Math.abs(new Date('10-13-2018') - new Date('09-13-2018'));
console.log(Math.ceil( timeDifference / (1000 * 60 * 60 * 24)));
new Date('10-13-2018') - new Date('09-13-2018') will give you 2592000000 milliseconds, since time is represented as Unix time. you can check unix time of any date by doing following.
console.log(new Date().getTime('10-13-2018'));
now the calculations behind the scene is 2592000000 / 1000*60*60*24 (that is total milliseconds in one day) = 30 days
I have requirement to calculate jday in javascript , for doing client side validation , Can any one help me how to calculate JDAY in javascript or script to change given JDAY to actual date or vice versa .
To know what is JDay ,I found the following site ,
http://www.pauahtun.org/Software/jday.1.html
Am also refering the below site for calculation which is mentioned in JAVA
http://www.rgagnon.com/javadetails/java-0506.html
Thank you in advance
Julian Day
The Julian Day is the number of elapsed days since the beginning of a cycle of 7980 years.
Invented in 1583 by Joseph Scaliger, the purpose of the system is to make it easy to compute an integer (whole number) difference between one calendar date and another calendar date.
The 7980 year cycle was derived by combining several traditional time cycles (solar, lunar, and a particular Roman tax cycle) for which 7980 was a common multiple.
The starting point for the first Julian cycle began on January 1, 4713 B.C. at noon GMT, and will end on January 22, 3268 at noon GMT, exactly 7980 whole days later.
As an example, the Julian day number for January 1, 2016 was 2,457,389, which is the number of days since January 1, 4713 B.C. at that day.
How to calculate it
As we know that Unix time is the number of seconds since 00:00:00 UTC, January 1, 1970, not counting leap seconds, and also called Epoch, we can use some math to calculate the Julian Day when we already have the Unix time.
GMT and UTC share the same current time in practice, so for this, there should be no difference.
To start with, we need to know the number of days from when the Julian cycle began, until Unix timestamps began.
In other words, the number of days from January 1, 4713 B.C. at 12:00:00 GMT, until January 1, 1970 at 00:00:00 UTC.
Having this set number of days, that never change, we can just add the number of days from January 1, 1970 until today, which is what Javascript returns anyway, to get the Julian Day.
Without adding up all those years, but simply by searching the web, it tells us that the difference in days between the year 4713 B.C. and 1970 A.D. is 2440588 days, and because the Julian Cycle began at noon, not at midnight, we have to subtract exactly half a day, making it 2440587.5 days.
So what we have now is 2440587.5 days + UNIX TIME in days === Julian Day
With some simple math we can figure out that a day is 86,400 seconds long, and the Unix timestamp is in milliseconds when using Javascript, so UNIX TIME / 86400000 would get us the number of days since Thursday, 1 January 1970, until today.
Now for just the day, we wanted the whole number of days, and not the fractional, and can just round it down to the closes whole day, doing something like
Math.floor((UNIX TIME / 86400000) + 2440587.5);
Julian Date
Sometimes in programming, a "Julian Date" has come to mean the number of days since the year started, for instance June 1, 2016 would be 152 days into that year etc.
The correct use of "Julian Date" is a Julian Day with a timestamp added as a fractional part of the day.
Taking the example at the top of this answer, where January 1, 2016 was the Julian Day 2,457,389 , we can add a time to that.
The Julian Day starts at noon, with no fractional time added, and so at midnight it would be 2457389.5 and at 18:00, or six hours after noon, it would be 2457389.25, adding "half a day", "quarter of a day" etc.
Calculating it, again
This means 0.1 Julian Date is the same as 24 hours divided by 10, or 24 / 10 === 2.4 hours, or in other words, Julian Day timestamps are fractional with decimals (one tenth of a day etc).
Lets look at some Javascript functions, firstly the Date constructor.
Javascript only has access to the local time on the computer it runs on, so when we do new Date() it does not neccessarely create an UTC date, even if UNIX time is in UTC, new Date gives you the number of seconds from epoch until whatever local time your computer has, and does not take your timezone into consideration.
Javascript does however have Date.UTC, which would return the date in UTC format, lets check the difference, and this will of course differ according to the timezone you've set the local system to.
var regular_date = new Date(2016, 1, 1, 0, 0, 0);
var UTC_date = Date.UTC(2016, 1, 1, 0, 0, 0);
var difference = UTC_date - regular_date;
document.body.innerHTML = 'The difference between your local time and UTC is ' +(difference/1000)+ ' seconds';
Remember the part at the begin of this chapter, about 0.1 Julian Date being the same as 24 hours divided by 10, or 24 / 10 === 2.4 hours, well, 2.4 hours is 144 minutes, and now lets look quickly at Javascripts getTimezoneOffset() method, the docs say
The getTimezoneOffset() method returns the time-zone offset from UTC,
in minutes, for the current locale.
So, it returns the offset for the systems timezone in minutes, that's interesting as most javascript methods that deal with dates returns milliseconds.
We know that a 1/10 of a day is 144 minutes, so 10/10, or a whole day, would be 1440 minutes, so we could use some math to counteract the local systems timezone, given in minutes, and divide it by the number of minutes in a day, to get the correct fractional value
So now we have
2440587.5 days + UNIX TIME in days === Julian Day
and we know Javascripts Date constructor doesn't really use UTC for the current date, but the system time, so we have to have
TIMEZONEOFFSET / 1440
joining them together we would get
(JAVASCRIPT TIME / 86400000) - (TIMEZONEOFFSET / 1440) + 2440587.5
// ^^ days since epoch ^^ ^^ subtract offset ^^ ^^days from 4713 B.C. to 1970 A.D.
Translating that to javascript would be
var date = new Date(); // a new date
var time = date.getTime(); // the timestamp, not neccessarely using UTC as current time
var julian_day = (time / 86400000) - (date.getTimezoneOffset()/1440) + 2440587.5);
Now this is what we should use to get the Julian Day as well, taking measures to remove the timezone offset, and of course without the fractional time part of the Julian Date.
We would do this by simpy rounding it down to the closest whole integer
var julian_date = Math.floor((time / 86400000) - (date.getTimezoneOffset()/1440) + 2440587.5));
And it's time for my original answer to this question, before I made this extremely long edit to explain why this is the correct approach, after complaints in the comment field.
Date.prototype.getJulian = function() {
return Math.floor((this / 86400000) - (this.getTimezoneOffset() / 1440) + 2440587.5);
}
var today = new Date(); //set any date
var julian = today.getJulian(); //get Julian counterpart
console.log(julian)
.as-console-wrapper {top:0}
And the same with the fracional part
Date.prototype.getJulian = function() {
return (this / 86400000) - (this.getTimezoneOffset() / 1440) + 2440587.5;
}
var today = new Date(); //set any date
var julian = today.getJulian(); //get Julian counterpart
console.log(julian)
.as-console-wrapper { top: 0 }
And to finish of, an example showing why
new Date().getTime()/86400000 + 2440587.5
doesn't work, at least not if your system time is set to a timezone with an offset, i.e. anything other than GMT
// the correct approach
Date.prototype.getJulian = function() {
return (this / 86400000) - (this.getTimezoneOffset() / 1440) + 2440587.5;
}
// the simple approach, that does not take the timezone into consideration
Date.prototype.notReallyJulian = function() {
return this.getTime()/86400000 + 2440587.5;
}
// --------------
// remember how 18:00 should return a fractional 0.25 etc
var date = new Date(2016, 0, 1, 18, 0, 0, 0);
// ^ ^ ^ ^ ^ ^ ^
// year month date hour min sec milli
var julian = date.getJulian(); //get Julian date
var maybe = date.notReallyJulian(); // not so much
console.log(julian); // always returns 2457389.25
console.log(maybe); // returns different fractions, depending on timezone offset
.as-console-wrapper { top: 0 }
new Date().getTime()/86400000 + 2440587.5
will get the unix time stamp, convert it to days and add the JD of 1970-01-01, which is the epoch of the unix time stamp.
This is what astronomers call julian date. It is well defined. Since neither Unix time stamp nor JD take leap seconds into account that does not reduce the accuracy. Note that JD need not be in timezone UTC (but usually is). This answer gives you the JD in timezone UTC.
According to wikipedia:
a = (14 - month) / 12
y = year + 4800 - a
m = month + 12a - 3
JDN = day + (153m + 2) / 5 + 365y + y/4 - y/100 + y/400 - 32045
If you're having a more specific problem with the implementation, provide those details in the question so we can help further.
NOTE : This is not correct because the "floor brackets" on Wiki were forgotten here.
The correct formulas are:
a = Int((14 - Month) / 12)
y = Year + 4800 - a
m = Month + 12 * a - 3
JDN = Day + Int((153 * m + 2) / 5) + 365 * y + Int(y / 4) - Int(y / 100) + Int(y / 400) - 32045
JD =>
const millisecondsSince1970Now = new Date+0
const julianDayNow = 2440587.5+new Date/864e5
const dateNow = new Date((julianDayNow-2440587.5)*864e5)
There seems to be confusion about what a Julian-Day is, and how to calculate one.
Javascript time is measured as GMT/UTC milliseconds UInt64 from Jan 1, 1970 at midnight.
The Month, Day, Year aspects of the JavaScript Date function are all implemented using Gregorian Calendar rules. But Julian "Days" are unaffected by that; however mapping a "day-count" to a Julian Month, Day, Year would be.
Calculating Julian-Day conversions are therefore a relative day count from that point in time (Jan 1, 1970 GMT/UTC Gregorian).
The Julian-Day for Jan 1, 1970 is 2440587.5 (0.5 because JulianDays started at NOON).
The 864e5 constant is JavaScript notation for 86,400,000 (milliseconds/day).
The only complexities are in calculating Julian dates (days) prior to adoption of the 1582 Gregorian calendar whose changes mandated from Pope Gregory were to correct for Leap Year drift inaccuracies affecting Easter. It took until around 1752 to be fully adopted throughout most countries in the world which were using the Julian Calendar system or a derivative (Russia and China took until the 20th century).
And the more egregious errors in the first 60 years of Julian date implementation from Julius Caesar's 46BC "reform" mandate where priests made mistakes and people misunderstood as they folded a 14/15 month calendar. (hence errors in many religious dates and times of that period).
🎪 None of which applies in JavaScript computation of Julian Day values.
See also: (from AfEE EdgeS/EdgeShell scripting core notes)
Astronomy Answers - Julian Day Number (multi-calendrical conversions)
Julian calendar
Atomic Clocks
JavaScript operator precedence
Microsoft FILETIME relative to 1/1/1601 epoch units: 10^-7 (100ns)
UUID/GUIDs timestamp formats - useful for time-date conversion also
"Leap Second" details
There is a separate subtlety "leap-second" which applies to astronomical calculations and the use of atomic clocks that has to do with earth orbital path and rotational drift.
i.e., 86,400.000 seconds per day needs "adjustment" to keep calendars (TimeZones, GPS satellites) in sync as it is currently 86,400.002.
It seems that the final code given in the accepted answer is wrong. Check the "official" online calculator at US Naval Observarory website:
http://aa.usno.navy.mil/data/docs/JulianDate.php
If someone knows the correct answer to a answer time and calendar, it's USNO.
Additionally, there is an npm package for this:
julian
Convert between Date object and Julian dates used in astronomy and history
var julian = require('julian');
var now = new Date(); // Let's say it's Thu, 21 Nov 2013 10:47:02 GMT
var jd = '';
console.log(jd = julian(now)); // -> '2456617.949335'
console.log(julian.toDate(jd)); // -> Timestamp above in local TZ
https://www.npmjs.com/package/julian
Whatever you do, DON'T USE getTimezoneOffset() on dates before a change of policy in the current Locale, it's completely broken in the past (it doesn't apply iana database rules).
For example, if I enter (UTC date 1st of october 1995 at 00:00:00):
var d=new Date(Date.UTC(1995, 9, 1, 0, 0, 0)); console.log(d.toLocaleString()); console.log(d.getTimezoneOffset());
in the javascript console in Chrome, it prints (I'm in France):
01/10/1995 at 01:00:00 <= this is winter time, +1:00 from UTC
-120 <= BUT this is summer time offset (should be -60 for winter)
Between 1973 and 1995 (included), DST (-120) terminated last Sunday of September, hence for 1st of October 1995, getTimezoneOffset() should return -60, not -120. Note that the formatted date is right (01:00:00 is the expected -60).
Same result in Firefox, but in IE and Edge, it's worse, even the formatted date is wrong (01/10/1995 02:00:00, matching the bad -120 result of getTimezoneOffset()). Whatever the browser (of these 4), getTimezoneOffset() uses the current rules rather than those of the considered date.
Variation on the same problem when DST didn't applied in France (1946-1975), Chrome console:
d=new Date(Date.UTC(1970, 6, 1, 0, 0, 0)); console.log(d.toLocaleString()); console.log(d.getTimezoneOffset());
displayed:
01/07/1970 01:00:00 <= ok, no DST in june 1970, +1:00
-120 <= same problem, should be -60 here too
And also, same thing in Firefox, worse in IE/Edge (01/07/1970 02:00:00).
I did this for equinox and solistice. You can use the function for any Julian date.
It returns the Julian date in the calender date format: day/month.
Include year and you can format it anyway you want.
It's all there, year, month, day.
Since Equinox and Solistice are time stamps rather than dates, my dates in the code comes back as decimals, hence "day = k.toFixed(0);". For any other Julian date it should be day = k;
// For the HTML-page
<script src="../js/meuusjs.1.0.3.min.js"></script>
<script src="../js/Astro.Solistice.js"></script>
// Javascript, Julian Date to Calender Date
function jdat (jdag) {
var jd, year, month, day, l, n, i, j, k;
jd = jdag;
l = jd + 68569;
n = Math.floor(Math.floor(4 * l) / 146097);
l = l - Math.floor((146097 * n + 3) / 4);
i = Math.floor(4000 * (l + 1) / 1461001);
l = l - Math.floor(1461 * i / 4) + 31;
j = Math.floor(80 * l / 2447);
k = l - Math.floor(2447 * j / 80);
l = Math.floor(j / 11);
j = j + 2 - 12 * l;
i = 100 * (n - 49) + i + l;
year = i;
month = j;
day = k.toFixed(0); // Integer
dat = day.toString() + "/" + month.toString(); // Format anyway you want.
return dat;
}
// Below is only for Equinox and Solistice. Just skip if not relevant.
// Vernal Equinox
var jv = A.Solistice.march(year); // (year) predefined, today.getFullYear()
var vdag = jdat(jv);
// Summer Solistice
var js = A.Solistice.june(year);
var ssol = jdat(js);
//Autumnal Equinox
var jh = A.Solistice.september(year);
var hdag = jdat(jh);
// Winter Solistice
var jw = A.Solistice.december(year);
var vsol = jdat(jw);
Well, you might think that this question has already been asked, but I think it has not. The solutions I've read about all had this "jigsaw puzzle" technique (like getUTCMonth() + getUTCMinutes + ...).
But as I only want to compare the elapsed seconds between two UTC (!) dates, this does not apply.
As everybody knows, you can get the current (non-UTC) date by:
var d = new Date();
var t_millis = d.getTime();
But this is NOT what I want. I'd like to have the current system date in UTC and in milliseconds, so not mess about with strings at all. AFAIK the variable t_millis will contain the millisecond value of the current timestamp in GMT, not UTC.
(Since d is in GMT as well. Unless getTime() does a sort of implicit time zone conversion, i. e. adding the offset BEFORE giving out the milliseconds, but I've never read about that anywhere)
So is there really no other way than adding the offset to the time value?
I'm desperately missing a function like getUTCTimeMillis() known from other languages.
This is an old question but for the sake of the new visitors here is THE CORRECT ANSWER:
Date.now();
It returns the number of milliseconds elapsed since 1 January 1970 00:00:00 UTC
The millisecond value of the time-of-day is going to be the same regardless of your time zone. That is, there are no time zones on planet Earth that differ from one another by a number of milliseconds greater than zero. (They may differ by an integer number of hours or even minutes, but not seconds or milliseconds.)
That said, the value you get back from getTime() is a UTC-relative timestamp. If two web browsers at widely different spots on the globe create a Date object at the same time, they'll both get the same value from .getTime() (assuming the clocks are synchronized, which is of course highly unlikely).
Here: 1338585185539 That's a timestamp I just got from my browser. I'm in Austin, TX, and now it's 4:13 in the afternoon (so that timestamp will be from slightly before that). Plug it into a Date instance on your machine and see what it says.
(edit — for posterity's sake, that timestamp is from 1 June 2012.)
how about:
var now = new Date();
var utc_now = new Date(now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate(), now.getUTCHours(), now.getUTCMinutes(), now.getUTCSeconds(), now.getUTCMilliseconds());
console.log('UTC: ' + utc_now) // correct UTC time but wrong timezone!
console.log('UTC (in ms): ' + utc_now.getTime())
I have used this function to solve the problem.
function getUTCNow()
{
var now = new Date();
var time = now.getTime();
var offset = now.getTimezoneOffset();
offset = offset * 60000;
return time - offset;
}
The getTime function returns the number of milliseconds elapsed since
1 January 1970 00:00:00 in the client timezone.
getTimezoneOffset return offset in minutes between Client timezone and UTC.
offset = offset * 60000; this operation transform minutes in miliseconds.
subtracting the offset get the number of milliseconds elapsed since 1
January 1970 00:00:00 UTC.
To get the timestamp from a date in UTC, you need to take in consideration the timezone and daylight savings for that date. For example, a date in January or in July could mean 1 hour difference.
The option below does just that.
Date.prototype.getUTCTime = function () {
return this.getTime() - (this.getTimezoneOffset() * 60000);
};
It can be used as in:
var date = new Date();
var timestamp = date.getUTCTime();