How to add timezone offset to string without changing the time?

Question

I have a time string like this 2021-12-29T01:30:00.105Z . I want to add offset for a timezone without changing the date and time. So it should look like this after conversion - 2021-12-29T01:30:00+08:00 for "Asia/Kuala_Lumpur" timezone.

So 2021-12-29T01:30:00.105Z -> 2021-12-29T01:30:00+08:00

I cannot do a string replace since the timezone will be dynamic and does not always has to be "Asia/Kuala_Lumpur".

I am using moment and moment-timezone libraries and have tried different ways to get the required result but none seems to work.

Please help.

Answer 1

If you have the IANA name for the timezone and you want to change the timezone of a date in +XX:XX format without modifying the time, you can calculate the offset and replace it in the string:

 const timeString = '2021-12-29T01:30:00.105Z'; const timezone = 'Asia/Kuala_Lumpur'; const offset = Intl.DateTimeFormat([], {timeZone: timezone, timeZoneName: 'longOffset'}).formatToParts().find(o => o.type === 'timeZoneName').value.match(/\+.*$/)[0]; const newTimeString = timeString.replace(/\..+Z$/, offset); console.log(timeString); console.log(newTimeString);