Datetime conversion to UTC from selected timezone [duplicate]-CodePudding

I have developed a page where users can filter records based on their selections in the filters. The datetime picker allows users to select a specific datetime and a dropdown allows the user to select the time zone in which they want that selected date to be converted to UTC.

For example, on my computer the time zone set is Asia/Karachi which has an offset of 5 UTC. But I want to select Europe/Prague from the dropdown and 09/14/2021 3.30pm as the date time. The time should be converted to 1.20 PM as Europe/Prague has a time offset of 2 from UTC using below code.

var ddate = new Date(date.toLocaleString('en-US', {
    timeZone: 'Europe/Prague'
  }));

However, this yields 12.30 PM as the time. Apparently it is converting from Asia/Karachi(my computer time zone) to Europe/Prague. But I want the selected datetime to be converted to UTC based on the time zone the user selects from the dropdown of available time zones. Is there any possible solution? I have tried researching and coding a lot but haven't found any yet.

CodePudding user response：

Have you tried moment & moment-timezone? maybe something like this:

import moment from "moment";
const myDate = "09/14/2021 3:30 PM";
const myTimeZone = "Europe/Prague";

let convertedTime = moment.tz(myDate, time_zone).format();

and you can set your format to be ("HH:mm A")

CodePudding user response：

If you want a date constructor for specific timezones make use of new Date('YYYY-MM-DDTHH:NN:SS.sss±HH:NN').

What you describe and want, is what Date already does if you generate a Date using new Date('YYYY-MM-DDTHH:NN:SS.sss±HH:NN'). You simply have to use it in this format.

±HH:NN is timezone information from your timezone-dropdown. It can either start with a or a -. (Take a look at the 3rd snippet)

Other formats as the ones i mentioned, are invalid if passed to the Date constructor and you may get unexpected results.

The dropdown (the one about the timezone) requires the information of hrs:mins and -hrs:mins respective to the timezone selected.

The following describes the Date constructor.

Don't pass a formated string like this to new Date() - it's invalid.

If you use new Date() you either have to pass a time value in milliseconds, a date only or an ISO Timestamp.

new Date(date.valueOf()) results in a copy
new Date(date.toISOString()) results in a copy
new Date(date.toJSON()) results in a copy
new Date(date.toDateString()) results in a copy of the date only => no hour GMT 0 on the current day.

All examples above (except the last one) are a copy of the original date.

For more information on the arguments supported by the Date-constructor take a look at Date.parse()#Date Time String Format

There is no need to change anything. If it's midnight at Asia/Karachi, it will be 9pm (21:00) in Europe/Prague.

As you can see on this example, use GMT 0 or any other accepted Time-Zone String.

Examples of different arguments

1

const date = new Date("2021-02-14T00:00:05.000 00:00"); // 5 seconds after midnight on February 14th, 2021 GMT 0

["GMT 0", "UTC", "America/New_York", "Europe/Madrid", "Europe/Prague", "Europe/Moscow", "Asia/Karachi", "Asia/Tokyo", "PRC"].forEach(timeZone => {
  console.log(timeZone, date.toLocaleString('en-US', { timeZone }))
});

2

const date = new Date("2021-09-14");
["GMT 0", "UTC", "America/New_York", "Europe/Madrid", "Europe/Prague", "Europe/Moscow", "Asia/Karachi", "Asia/Tokyo", "PRC"].forEach(timeZone => {
  console.log(timeZone, date.toLocaleString('en-US', { timeZone }))
});

3

// 16:00 at timezone  9 is 7 am at gmt
const date = new Date("2021-09-14T16:00:00.000 09:00");
["GMT 0", "UTC", "America/New_York", "Europe/Madrid", "Europe/Prague", "Europe/Moscow", "Asia/Karachi", "Asia/Tokyo", "PRC"].forEach(timeZone => {
  console.log(timeZone, date.toLocaleString('en-US', { timeZone }))
});