Develop Reference

How do I convert UTC DateTime to local DateTime without ending up with a different format

I have specific DateTime values in this format 'YYYY-MM-DDThh:mm:ss.ms' (e.g. '2022-05-10T13:44:00.0000000') and I need to convert them to local DateTime (which is UTC+2 for me) without changing the format (so '2022-05-10T15:44:00.0000000' is the desired result (even better would be without the milliseconds but that would just be the icing on the cake)).
I've searched far and wide but every alleged solution I find either changes the format or doesn't change the time at all.
This is what I have right now, it successfully converts the time to local time but by running it through .toISOString() to get the original format back it converts it back to UTC time.
//Input: event.start.dateTime = '2022-05-10T13:44:00.0000000'
let startDateTime = new Date(event.start.dateTime);
startDateTime.setMinutes(startDateTime.getMinutes() -
startDateTime.getTimezoneOffset());
document.getElementById('ev-start').value =
startDateTime.toISOString().slice(0,16);
//Output: '2022-05-10T13:44:00.000Z'

I couldn't find a clean and satisfying solution so I decided to just to the formatting myself. Here's what I ended up with:
Input: '2022-05-10T13:44:00.0000000'
let startDateTime = new Date(event.start.dateTime);
startDateTime.setMinutes(startDateTime.getMinutes() -
startDateTime.getTimezoneOffset());
let localStartDateTime = startDateTime.getFullYear() + "-" +
(startDateTime.getMonth() + 1).toString().padStart(2, '0') +
"-" + startDateTime.getDate().toString().padStart(2, '0') +
"T" + startDateTime.getHours().toString().padStart(2, '0') +
":" + startDateTime.getMinutes().toString().padStart(2, '0')
+ ":" +
startDateTime.getSeconds().toString().padStart(2, '0');
document.getElementById('ev-start').value =
localStartDateTime;
Output: '2022-05-10T15:44:00'

Hope this helps
const startDateTime = new Date('2022-05-10T13:44:00.0000000');
const outputDateTime = new Date(startDateTime.toString()).toISOString().slice(0, 19);
//document.getElementById('ev-start').value = outputDateTime
console.log(outputDateTime);

moment.js | check isBefore getting confused with date

I'm currently working with a project where I need to find if a time in HH:mm is before another time.
I am using moment time zone and setting the time zone globally to UTC.
The date which I am comparing is: 2020-09-02T00:00:00.0000+00:00
I am running a check where I am doing the following:
const example = '2020-09-02T00:00:00.0000+00:00'
const time = moment(example)
const timeStart = moment('08:00', 'HH:mm')
console.log(time.isBefore(timeStart))
The console log returns a result of false.
The reason I believe is that the timeStart is evaluating to the current day, so it's failing due to the date being in the future. I need to stop moment from comparing the date, is there a way to do this?
What I am trying to achieve is something of the following
'00:00:00'.isBefore('08:00')
const time = moment('2020-09-02T00:00:00.0000+00:00')
const timeStart = moment('08:00', 'HH:mm')
console.log(time)
console.log(timeStart)
console.log(time.isBefore(timeStart))
<script src="https://cdn.jsdelivr.net/momentjs/2.13.0/moment.min.js"></script>

You can do this with moment.js by converting the timestamp to a moment object, then cloning the object and setting its time to the required comparison time. That way you're always comparing times on the same date.
To keep everything as UTC, use utc. E.g.
let ts = '2020-09-02T00:00:00.0000+00:00';
let d = moment.utc(ts); // Invoke UTC mode
let time = '08:30';
let [h, m] = time.split(':');
let e = d.clone().hours(h).minutes(m).seconds(0).milliseconds(0);
console.log(d.format() + ' is before\n' +
e.format() + '? ' + d.isBefore(e));
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.27.0/moment.min.js"></script>
You can compare just the time with plain JS fairly easily:
/**
* Compare a time to just the time part of a
* Date, all using UTC.
*
* #param {Date} date - date to compare
* #param {string} time - time in HH:mm format
* #returns {boolean} true if time in date is before time passed to function
*/
function isTimeBefore(date = new Date(), time) {
// Get time value for start of UTC day
// Copy date so don't affect original
let dayStart = new Date(+date).setUTCHours(0,0,0,0);
// Convert the time to milliseconds since midnight
let [h, m] = time.split(':');
let ms = h*3.6e6 + m*6e4;
// Compare to the date's milliseconds elapsed since midnight
return ms > (date - dayStart);
}
// UTC timestamp
let ts = '2020-09-02T00:00:00.0000+00:00';
// Convert to Date
let d = new Date(ts);
// local time
let time = '08:30';
console.log('UTC: ' + d.toISOString() + '\nis before ' + time + ' UTC? : ' + isTimeBefore(d, time));
The built–in parser should generally be avoided, however the above uses it to convert the timestamp to a Date because it's about the only supported format that is reliably parsed by browsers in use.

const time = moment('2020-09-02T00:00:00.0000+00:00')
const timeStart = moment('09:00', 'HH:mm')
time.isBefore(timeStart) //returns true
returns true to me.

Comparing 2 strings with number values JS

Im trying to check to see if current time is lower than time that is responded from an API. Problem is they are both strings. The API response contains characters such as : and -, so parseInt is not working (at least that's my theory why its not working)
var d = new Date();
var hour = d.getHours();
var minutes = d.getMinutes();
var year = d.getFullYear();
var month = d.getMonth() +1;
var day = d.getDate();
var seconds = d.getSeconds();
var time = year+'-'+month+'-'+day+' '+hour+':'+minutes+':'+seconds;
time returns
"2016-11-7 15:48:2"
API Response is
"2016-11-07 20:06:00"
I have confirmed they are both strings
time < APIresponse
Always returns false
Are there any known solutions? Thanks in advance.

Preface: Timezone
Your current code assumes that the date/time you're getting from the API is in "local time," because you're comparing it with the current date/time in the browser's local timezone. APIs frequently provide date/times in UTC rather than "local" time, so beware of that assumption and double-check it.
If you want to do it at the string level
...you need to ensure when building time that you zero-pad the numbers, so for instance not just 7 for the day of the month, but 07. Then you'll end up with strings that have the fields in a valid comparable order (because the most significant field [year] is first, and the least significant field [seconds] is last), so a lexicographic comparison of the strings is valid.
So for instance, you'd create time like this:
var time = pad(year, 4) + '-' + pad(month, 2) + '-' + pad(day, 2) + ' ' + pad(hour, 2) + ':' + pad(minutes, 2) + ':' + pad(seconds, 2);
...where pad is a function you define that adds as many 0s as needed to ensure the string is as long as the second argument defines.
Then you can do:
if (time < timeStringFromAPI)
Note: If the API's response is giving you the date/time in UTC rather than local time, you'll need to use the UTC version of the accessor functions (e.g., getUTCHours, getUTCFullYear, etc.) rather than the ones you're using, which are for local time.
If you want to do it at the date level
...then you need to convert the date you're getting from the API to a Date. It's almost in a form you can reliable parse on modern browsers,
but not quite; some browsers will parse that string as local time, others as UTC.
If you're sure it's in local time, then the best thing to do is split it into its parts and use the multipart Date constructor:
var parts = timeStringFromAPI.split(/[-:]/);
var apiDate = new Date(
+parts[0], // Year
+parts[1] - 1, // Month
+parts[2], // Day
+parts[3], // Hours
+parts[4], // Minutes
+parts[5] // Seconds
);
If you're sure it's in UTC, then you can either do the above but with new Date(Date.UTC(...)) rather than just new Date(...), or you can put the string into the JavaScript date/time format and parse that:
var apiDate = new Date(timeStringFromAPI.replace(" ", "T") + "Z");
That takes the "2016-11-07 20:06:00" and changes it to "2016-11-07T20:06:00Z", which can reliably be parsed on all non-obsolete browsers.
Then you can do
if (new Date() < apiDate) {

try this :
var curDate = new Date();
then compare in this way
if (new Date(yourdate) <= curDate)
{
something...
}

var d1 = "2016-11-7 15:48:2";
var d2 = "2016-11-07 20:06:00";
if (new Date(d1) < new Date(d2)) {
alert('true')
}

Safe time comparison in Moment.js

In current scenario it is safe to assume that all compared dates are of the same day, so only time is stored.
However, it is evident that there is non-zero probability of Y2K-like problem.
This piece of code may fail when being executed at 00:00 (roughly) if momentTimeA line is evaluated at 23:59:59.999 of one day and momentTimeB line is evaluated at 00:00:00.000 of another day:
// timeA is '06:00:00', momentTimeA is '2016-11-11T06:00:00.000';
const momentTimeA = moment(timeA, 'H:mm:ss');
// ...
// timeB is '03:00:00', momentTimeB is '2016-11-12T03:00:00.000';
const momentTimeB = moment(timeB, 'H:mm:ss');
// should be positive
momentTimeA.diff(momentTimeB);
Currently this code that does time comparisons runs synchronously, but it may become asynchronous later, this will considerably increase the risk.
How this problem should be addressed?

Since you are dealing with a time range that might cross over midnight, and you're not accounting for dates, then you will need to detect and adjust for this on your own.
// your inputs
var timeA = '06:00:00';
var timeB = '03:00:00';
// today's date as a string
var today = moment().format('YYYY-MM-DD');
// both moments created using the same date
var momentTimeA = moment(today + ' ' + timeA, 'YYYY-MM-DD H:mm:ss');
var momentTimeB = moment(today + ' ' + timeB, 'YYYY-MM-DD H:mm:ss');
// check if midnight is crossed
if (momentTimeA.isAfter(momentTimeB)) {
// move A back a day (this is an assumption!)
var yesterday = moment().subtract(1, 'day').format('YYYY-MM-DD');
momentTimeA = moment(yesterday + ' ' + timeA, 'YYYY-MM-DD H:mm:ss');
}
// now you can take the difference
var delta = momentTimeB.diff(momentTimeA);
Note you had A and B reversed in your original diff. Assuming A comes first, use B.diff(A) to get a positive result.
Also, note that in the above code, it's important that you don't just subtract a day from the moment to adjust it, but that you re-create a new moment on yesterday at the given time. This is because you are working in local time, which could possibly have a DST transition on one of the times provided.

difference between date with and without time portion

let's say that I have two variables: one that contains a date string (without time) and another one that contains the same date string but with time 00:00:00 like this:
var date1 = '2013-10-23';
var date2 = '2013-10-23 00:00:00';
var date1_time = new Date(date1).getTime();
var date2_time = new Date(date2).getTime()
console.debug('Date 1 time: ' + date1_time + "\n" + 'Date 2 time: ' + date2_time);
The result in the console is this:
Date 1 time: 1382486400000
Date 2 time: 1382500800000
Why aren't these two equal to the same thing? Shouldn't date1's time portion default to 00:00:00 since I did not put a time?
Thank you

I just tested it on chrome and found out that
The first one gives you the timestamp for 00:00:00 UTC
The second gives you timestamp with your current timezone.
So if you substract them you will see +-your timezone:
var date1_time = new Date(date1).getTime();
var date2_time = new Date(date2).getTime();
console.log((date2_time-date1_time)/1000/60/60); //will print the timezone difference.

You can get exact what time the first variable is considering.
var timestamp = 1382486400000;
var date = new Date();
date = new date(timestamp + date.getTimezoneOffset() * 60000)
alert(date);
It all happens because of default UTC time zone and your current
timezone.