Hello,

I have a datepicker and it shows me example this:

Sun May 04 2025 15:30:00 GMT+0200 (Mitteleuropäische Sommerzeit)

if I send it to my backend with fetch in the network list it shows this:

2025-05-04T13:30:00

two hours different but I want to remove the timezone how I do it ?

let startTime = picker.value();

const send = async () => { 
  const res = await fetch('https://backend...', {
     method: 'POST',
  headers: {
    'Content-type': 'application/json; charset=UTF-8',
  },
  body: JSON.stringify({
    startTime
  }),
})
.....
},

I tried this

startTime.toISOString().slice(0, 19)

but not works it shows correctly in console.log but after send to my backend in the network tab in chrome it shows this:

2025-05-04T13:30:00

but it should be 15:30

We are trying to add times to our dates in an older app and the dates were almost always stored as partially formed ISO strings. Not a hard rule since times were never used before.

Now I need to start displaying the times with the dates and allowing the user to alter the times on the front end.

Example: we get a date ISO string from the backend as 2008-08-15T00:00:00.

When I create a Date object from it, I get the date in my local time zone (GMT-0600). In this example, Fri, August 15, 2008 00:00:00 (GMT-0600).

Then later when the edit form is submitted with no change to the day or time, I convert the Date object to an ISO string and strip the milliseconds and time zone code to keep it consistent with the current format in the database. In this example it returns 2008-08-15T06:00:00 to the backend.

Notice the time was provided as 00:00:00 but after parsing it and then converting to an ISO string, I've now added 6 hours to the time and am returning 06:00:00.

I am thinking I could convert it to GMT-0000 before converting to an ISO string but I'm not sure if that is the cleanest solution. Has anyone else had a similar scenario and what would you suggest to do to make this work (that doesn't include altering all the dates in the DB, we're planning for that down the road)?

My most frustrating programming woes ever have been managing different timezones. How do you all handle these situations effectively?

In my app, I have data sources from many places. Then I aggregate that data in terms like month-to-date, today, etc. However, these all have different definitions depending what timezone the user is in. So when someone queries the API from the frontend, how do you make sure their month-to-date makes the most sense to their timezones?

I am currently using Luxon to do transformations like start of month, and end of month for database conversions. However Luxon on the server will do the start and end based on the server timezone. I could set it to another, but then I would have to report on specifically what that is. I can't do simple offsets, as I would still have to account for daylight savings etc. Even with packages this feels like insanity.

when I set a date using a calander libary and save it in my localstorage as date.toISOString().split("T")[0] and after reloading the page, I retrieve from the localstorage and set in my local variable with new Date(date), it sets the time 1 day backward. I'm guessing its because the timezone i'm using is US and since US is 7 hours behind UTC, so new Date() treats the argument as a UTC time and converts it into a local time?, how do I configure it to give me the exact date I stored in my localstorage?

What is best practice when dealing with date values without time, in JavaScript? My concern is subtle off-by-one bugs caused by local Time Zone (TZ) offset (e.g. +5 hours), when doing date math.

JavaScript's built-in Date type represents a date and time not just the date. Internal representation is an integer of microseconds since 1970-01-01 00:00:00 UTC. Other languages, like Python, have separate Date and DateTime types. Java 8 introduced LocalDate.

You also have things like: new Date('5/18/2020') is local TZ (in US), but new Date('2022-05-18') is UTC. Same with Date.parse(string). And the time zone on most servers in UTC, whereas on the browser side the time zone will vary.

The date values will be used for simple date math in code and will be stored in a SQL database.

Possibilities:

1. Use the an alternate type like integer value, of milliseconds or days (since 1970-01-01), or string in YYYYMMDD format.

2. This was combined with #1

3. Use Date ignoring time (as 00:00 local TZ). Convert from/to UTC when reading/writing to database

4. Use Date with time as 00:00 UTC. Have to be careful not to mix with Date values in local TZ (e.g. now = new Date())

5. Use Date in local TZ, but convert to UTC when read/writing to database. This is a variant of #3.

6. Create a LocalDate class that enforces midnight.

7. Use a library. js-joda has LocalDate.

I am leaning towards #3 and #6. Some code I am writing:

class LocalDate extends Date {
  // Error if time isn't midnight local TZ
  // Do not accept string in ISO format
  constructor(date?: Date|number|string)

  // Convert to 00:00 UTC
  // To be used before write to database
  toUtc(): Date

  // Only return date.  Also affects toJSON()
  toISOString(): string

  // Returns today's date at 00:00 Local TZ
  static today(): LocalDate
  // Set time to midnight local TZ, without error check.
  static fromDateTime(date: Date|number): LocalDate
  // Convert to local TZ.  Error if not 00:00 UTC.
  static fromUtc(date: Date|number): LocalDate
}

UPDATE:

Various edits.

Hi, I have been working on a little project where I create object keys from date timestamps.

The problem that is arising is that at March 24th - 25th when DST happens the values are no longer correct. How can I use a "dumb" date / calendar that does not have DST or Timezones?

const MILLISECONDS_IN_DAY = 86400000;

const FROM_MS = dateFns.startOfDay( from ).getTime();
const TO_MS = dateFns.startOfDay( to ).getTime();
const DIFF_IN_MS_BETWEEN_FROM_AND_TO = ( TO_MS - FROM_MS );
const MAX_MS = FROM_MS + DIFF_IN_MS_BETWEEN_FROM_AND_TO;

const day_bookings = {};

for ( let day_index = FROM_MS; day_index < MAX_MS; day_index += MILLISECONDS_IN_DAY ) {
    const current_day = dateFns.startOfDay( day_index );

    console.log( current_day );
    console.log( day_index, current_day.getTime() );
    console.log( day_index === current_day.getTime() );
    
    // won't be able to access later if timezone and/or DST is making the key unpredictable for me...
    day_bookings[ day_index ] = new DayBooking( current_day ); 

    ...

March 25th

Sun Mar 25 2018 00:00:00 GMT+0100 (Central European Standard Time)
1521932400000 1521932400000
true

March 26th

Mon Mar 26 2018 00:00:00 GMT+0200 (Central European Summer Time)
1522018800000 1522015200000
false