get client time zone from browser [duplicate]

Half a decade later we have a built-in way for it! For modern browsers I would use:

const tz = Intl.DateTimeFormat().resolvedOptions().timeZone;
console.log(tz);

This returns a IANA timezone string, but not the offset. Learn more at the MDN reference.

Compatibility table - as of March 2019, works for 90% of the browsers in use globally. Doesn't work on Internet Explorer.

Look at this repository pageloom it is helpful

download jstz.min.js and add a function to your html page

<script language="javascript">
    function getTimezoneName() {
        timezone = jstz.determine()
        return timezone.name();
    }
</script>

and call this function from your display tag

Often when people are looking for "timezones", what will suffice is just "UTC offset". e.g., their server is in UTC+5 and they want to know that their client is running in UTC-8.

In plain old javascript (new Date()).getTimezoneOffset()/60 will return the current number of hours offset from UTC.

It's worth noting a possible "gotcha" in the sign of the getTimezoneOffset() return value (from MDN docs):

The time-zone offset is the difference, in minutes, between UTC and local time. Note that this means that the offset is positive if the local timezone is behind UTC and negative if it is ahead. For example, for time zone UTC+10:00 (Australian Eastern Standard Time, Vladivostok Time, Chamorro Standard Time), -600 will be returned.

However, I recommend you use the day.js for time/date related Javascript code. In which case you can get an ISO 8601 formatted UTC offset by running:

> dayjs().format("Z")
"-08:00"

It probably bears mentioning that the client can easily falsify this information.

(Note: this answer originally recommended https://momentjs.com/, but dayjs is a more modern, smaller alternative.)

For now, the best bet is probably jstz as suggested in mbayloon's answer.

For completeness, it should be mentioned that there is a standard on it's way: Intl. You can see this in Chrome already:

> Intl.DateTimeFormat().resolvedOptions().timeZone
"America/Los_Angeles"

(This doesn't actually follow the standard, which is one more reason to stick with the library)

you could use moment-timezone to guess the timezone:

> moment.tz.guess()
"America/Asuncion"