Question 257656 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – How can I find offset of the timezone and get new zulu format of my date?

I am having the following zulu time

2023-09-04T00:00:00.000Z

this date is given as output from some library so I know that it is UTC time.
When the library gives that output I need to transform this timestamp time to my local time – because I know that my time is -120 minutes from the UTC the final output should be 2023-09-04T22:00:00.000Z.

Or let’s say that the library gives me this output 2023-09-10T23:59:59.590Z, I should convert it to 2023-09-10T21:59:59.590Z.

So I tried first to find out the timezone offset in minutes according to the local timezone of the user.
https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_gettimezoneoffset

In my case as I said it is -120 minutes. I can’t find a way how can I minus this 120 minutes of my initial timestamp and construct new timestamp.

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2

Answers


  1. 0

    The simplest way is to use toLocaleString with an appropriate language and offset.

    E.g. the following produces "2023-09-03 22:00:00 GMT−2".

    console.log(
  new Date('2023-09-04T00:00:00.000Z').toLocaleString('sv',{
    timeZone:'Etc/GMT+2',
    hour12:false,
    timeZoneName:'shortOffset'
  }
));

    The Etc offsets use the POSIX sense, so +2 is equivalent to GMT-2.

    Note that toLocaleString is not that reliable for formatting, better to use a library or your own formatting function (which might start with toLocaleString or Intl.DateTimeFormat to get the parts).

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  2. 0

    If you want to achieve what you describe here is one solution which might help you.

    1. convert the string to a Date object

    const time = new Date('2023-09-04T00:00:00.000Z')

    1. subtract the desired minutes

    time.setMinutes(time.getMinutes() - 120) // or however many you might want

    1. revert the subtracted time back into a human readable string

    const newTime = time.toISOString() // would print: 2023-09-03T22:00:00.000Z

    As other have mentioned already, this might not the best practice. You can write a function which can give you the correct datetime based on the locale (whether that would be from the browser or given as a parameter), or implement an already existing library which can do that for you.

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