Hướng dẫn nodejs get client timezone

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Syntax

Return value

The difference, in minutes, between the date as evaluated in the UTC time zone and as evaluated in the local time zone. The actual local time algorithm is implementation-defined, and the return value is allowed to be zero in runtimes without appropriate data.

Description

date.getTimezoneOffset() returns the difference, in minutes, between date as evaluated in the UTC time zone and as evaluated in the local time zone — that is, the time zone of the host system in which the browser is being used (if the code is run from the Web in a browser), or otherwise the host system of whatever JavaScript runtime (for example, a Node.js environment) the code is executed in.

Negative values and positive values

The number of minutes returned by getTimezoneOffset() is positive if the local time zone is behind UTC, and negative if the local time zone is ahead of UTC. For example, for UTC+10, -600 will be returned.

Varied results in Daylight Saving Time (DST) regions

In a region that annually shifts in and out of Daylight Saving Time (DST), as date varies, the number of minutes returned by calling getTimezoneOffset() can be non-uniform.

Note: getTimezoneOffset()'s behavior will never differ based on the time when the code is run — its behavior is always consistent when running in the same region. Only the value of date affects the result.

In most implementations, the IANA time zone database (tzdata) is used to precisely determine the offset of the local timezone at the moment of the date. However, if such information is unavailable, an implementation may return zero.

Examples

Using getTimezoneOffset()

// Create a Date instance for the current time
const currentLocalDate = new Date();
// Create a Date instance for 03:24 GMT-0200 on May 1st in 2016
const laborDay2016at0324GMTminus2 = new Date('2016-05-01T03:24:00Z-02:00');
currentLocalDate.getTimezoneOffset() === laborDay2016at0324GMTminus2.getTimezoneOffset();
// true, always, in any timezone that doesn't annually shift in and out of DST
// false, sometimes, in any timezone that annually shifts in and out of DST

getTimezoneOffset() and DST

In regions that use DST, the return value may change based on the time of the year date is in. Below is the output in a runtime in New York, where the timezone is UTC-05:00.

const nyOffsetSummer = new Date('2022-02-01').getTimezoneOffset(); // 300
const nyOffsetWinter = new Date('2022-08-01').getTimezoneOffset(); // 240

getTimezoneOffset() and historical data

Due to historical reasons, the timezone a region is in can be constantly changing, even disregarding DST. For example, below is the output in a runtime in Shanghai, where the timezone is UTC+08:00.

const shModernOffset = new Date('2022-01-27').getTimezoneOffset(); // -480
const shHistoricalOffset = new Date('1943-01-27').getTimezoneOffset(); // -540

This is because during the Sino-Japanese War when Shanghai was under Japanese control, the timezone was changed to UTC+09:00 to align with Japan's (in effect, it was a "year-round DST"), and this was recorded in the IANA database.

See also