Timezones are an integral part of working with dates and times on the web. Different parts of the world have different local times, and it is important to be able to manage this complexity when working with dates and times. Fortunately, there is a convenient way to manage this complexity in Javascript through the use of the Date object. In this article, we will explain what timezones are, how they work, and how to use Javascript to change timezone. With this information, you’ll be able to easily create and manage global dates and times.
What is Timezone and How Does it Work?
Timezone is a way of organizing time that is used around the world. It is used to determine when certain events (such as the beginning of a day, sunrise and sunset, etc.) occur locally. Timezones are based on the Greenwich Mean Time (GMT) offset, which is the number of hours difference between one time zone and another time zone. For example, the GMT offset for London is 0 hours, while the GMT offset for New York is -5 hours.
Timezones are important because they ensure that the same events are occurring simultaneously around the world. For example, when it is 11 AM in London, it is 6 AM in New York. Timezones help make sure that these events occur at consistent times across the globe.
Timezones are also important for international business and communication. By using the same timezone, businesses can coordinate meetings and events with people in different parts of the world. This helps to ensure that everyone is on the same page and that communication is efficient and effective.
Understanding the Different Timezones
There are 24 different timezones, each one representing 15 degrees of longitude relative to GMT-0. For example, GMT-1 represents 15 degrees west of the GMT baseline, GMT-2 represents 30 degrees west of the GMT baseline, and so on. Each timezone is represented by a three letter abbreviation (e.g. “PST” for Pacific Standard Time). Additionally, most countries observe Daylight Saving Time (DST), meaning that they temporarily shift their timezone forward or backward one hour.
In order to change a timezone in JavaScript, you need to be familiar with these timezone abbreviations. You can use the Date constructor to create Date objects in the desired timezone, and the getTimezoneOffset() method to get the number of minutes offset from GMT of any given Date object.
It is important to note that the timezone abbreviations are not standardized across all platforms. For example, the abbreviation for Central Standard Time (CST) is different in Windows than it is in Linux. Therefore, it is important to be aware of the platform you are working on when changing timezones in JavaScript.
Using JavaScript to Change Timezone
Using JavaScript, you can easily set, get and change timezones of Date objects. To convert a date from one timezone to another, all you need to do is create a Date object in the desired timezone, then use the setTimezoneOffset() method to set the Date object’s timezone offset.
For example, say we want to convert a date from Pacific Standard Time (PST) to Eastern Standard Time (EST). To do this, we can create a Date object in PST and then use the setTimezoneOffset() method to set its timezone:
var date = new Date(); //PSTdate.setTimezoneOffset(-300); //EST
The -300 is the amount of minutes difference between PST and EST. Once we set the timezone offset, we can use the .getTime() method to get the date and time in EST.
It is also possible to convert a date from one timezone to another using the toLocaleString() method. This method takes two parameters: the timezone and the format of the date. For example, to convert a date from PST to EST, we can use the following code:
var date = new Date(); //PSTdate.toLocaleString('en-US', {timeZone: 'America/New_York'}); //EST
Setting a Date Object’s Timezone
JavaScript also has a convenient way to create Date objects in different timezones: the Date.UTC() function. This function takes parameters for the year, month, day, hour, minute, second, and a numeric offset in minutes of where you want the Date object set (the offset represents the GMT offset).
var date = Date.UTC(2020, 0, 1, 10, 0, 0, -300); //date set in EST
The parameters are passed as numbers representing the values you want. The year is represented by a four digit number (2020), the month is represented by a zero indexed number (January is 0), and so on. The offset is represented by a number as well; for example, Eastern Standard Time has an -300 minute offset from GMT.
It is important to note that the Date.UTC() function returns the number of milliseconds since January 1, 1970, 00:00:00 UTC. This means that the Date object created with the Date.UTC() function will be set to the specified timezone, but the timezone will not be stored in the Date object itself. To get the timezone of the Date object, you must use the getTimezoneOffset() method.
Example 1: Converting Time from Tokyo to London
// Assume the current time in Tokyo
let tokyoTime = new Date().toLocaleString("en-US", { timeZone: "Asia/Tokyo" });
console.log("Current Time in Tokyo: " + tokyoTime);
// Convert Tokyo time to London time
let londonTime = new Date(tokyoTime).toLocaleString("en-US", { timeZone: "Europe/London" });
console.log("Corresponding Time in London: " + londonTime);
Explanation: This script first gets the current time in Tokyo and then converts it to the corresponding time in London. It demonstrates how to use the toLocaleString() method with the appropriate timezone settings.
Example 2: Converting Time from London to New York
// Assume a specific time in London
let londonTime = new Date('2023-11-28T15:00:00').toLocaleString("en-US", { timeZone: "Europe/London" });
console.log("Specific Time in London: " + londonTime);
// Convert London time to New York time
let newyorkTime = new Date(londonTime).toLocaleString("en-US", { timeZone: "America/New_York" });
console.log("Corresponding Time in New York: " + newyorkTime);
Explanation: Here, we are taking a specific time in London and converting it to the corresponding time in New York. This example is useful for scheduling meetings across these time zones.
Converting Between Timezones
Once you have a Date object in one timezone, you can easily convert it to another timezone by simply setting its timezone offset with .setTimezoneOffset(). For example, if you have a Date object in Eastern Standard Time and want to convert it to Pacific Standard Time, you simply need to set its offset to -300:
date.setTimezoneOffset(-300); //converting from EST to PST
It is important to note that the timezone offset is measured in minutes, so you will need to convert the timezone difference into minutes. For example, the time difference between Eastern Standard Time and Pacific Standard Time is three hours, which is equal to 180 minutes. Therefore, the offset for Pacific Standard Time is -300.
Working with Multiple Timezones
Working with multiple timezones can be difficult—luckily, there are libraries like moment-timezone that can help make it easier. Moment-timezone is an easy-to-use library for working with dates and times in various timezones. It has an intuitive API for converting dates between different timezones and for performing date calculations.
Moment-timezone also provides a comprehensive set of timezone data, which is regularly updated to ensure accuracy. This data can be used to display dates and times in the correct timezone, regardless of where the user is located. Additionally, moment-timezone can be used to detect the user’s timezone and automatically adjust the date and time accordingly.
Tips for Changing Timezone with JavaScript
- Use the
.getTimezoneOffset()method to get the number of minutes difference between two different timezones. - Always check if your time zone rules have changed before setting new timezone offsets.
- Always specify your local country code when setting dates and times. Not all countries observe Daylight Saving Time.
Common Pitfalls to Avoid When Changing Timezone
- Be sure to account for Daylight Saving Time when setting dates—not all countries observe Daylight Saving Time.
- Creating Date objects in one timezone and then converting to another can lead to unexpected results—it’s better to create it directly in the desired timezone.
- Be mindful of changes that may occur in Daylight Saving Time rules—it’s better to always check for changes before setting dates.
Conclusion
JavaScript’s Date object makes it easy to change between timezones in the browser. By understanding what timezones are and how they work, you can use JavaScript to manipulate dates and times in any time zone around the world. With a few simple lines of code and some knowledge of local time zone rules, you’ll be able to easily manage international dates and times with ease.
by the Bito team. 
