Introduction

When building applications used by people around the world, handling time zones becomes very important. A date and time displayed in one country may be different in another country because each location follows its own time zone.

JavaScript automatically works with the user’s local time zone but also provides methods for working with UTC (Coordinated Universal Time) and formatting dates for different regions.

For automation engineers, understanding time zones is essential when validating timestamps, testing global applications, verifying server responses, scheduling automated tests, comparing dates from different regions, and working with APIs that return UTC timestamps.

What is a Time Zone?

A time zone is a region of the world that observes the same standard time.

For example:

India follows Indian Standard Time (IST).
The United Kingdom uses Greenwich Mean Time (GMT) or British Summer Time (BST) depending on the season.
Japan follows Japan Standard Time (JST).
The United States has multiple time zones such as Eastern, Central, Mountain, and Pacific.

JavaScript automatically uses the time zone of the user’s computer unless otherwise specified.

Local Time vs UTC

There are two common ways to work with dates in JavaScript:

Local Time

Uses the user’s system time zone.

Example:

const now = new Date();

console.log(now.toLocaleString());

Sample Output

22/6/2026, 4:45:18 PM

UTC Time

Uses Coordinated Universal Time (UTC).

const now = new Date();

console.log(now.toUTCString());

Sample Output

Mon, 22 Jun 2026 11:15:18 GMT

Example 1: Display Local Date and Time

const today = new Date();

console.log(today.toLocaleString());

Sample Output

22/6/2026, 4:45:18 PM

Example 2: Display UTC Date and Time

const today = new Date();

console.log(today.toUTCString());

Sample Output

Mon, 22 Jun 2026 11:15:18 GMT

Example 3: Display ISO Date

const today = new Date();

console.log(today.toISOString());

Sample Output

2026-06-22T11:15:18.456Z

The Z at the end indicates UTC (Zulu Time).

Example 4: Get the Time Zone Offset

const today = new Date();

console.log(today.getTimezoneOffset());

Sample Output

-330

For India, the offset is typically -330 minutes, meaning IST is UTC+5:30.

Example 5: Display Date for Another Locale

const today = new Date();

console.log(today.toLocaleString("en-US"));

Sample Output

6/22/2026, 4:45:18 PM

Example 6: Display Date in a Specific Time Zone

const today = new Date();

console.log(
    today.toLocaleString("en-US", {
        timeZone: "Asia/Tokyo"
    })
);

Sample Output

6/22/2026, 8:15:18 PM

The displayed time depends on the specified time zone.

Common Time Zone Methods

Method	Description
`toLocaleString()`	Displays date and time in the local format
`toLocaleDateString()`	Displays the local date
`toLocaleTimeString()`	Displays the local time
`toUTCString()`	Displays the date and time in UTC
`toISOString()`	Returns the date in ISO 8601 format (UTC)
`getTimezoneOffset()`	Returns the difference between local time and UTC in minutes

Real-World Example

Display both local and UTC times.

const now = new Date();

console.log("Local:", now.toLocaleString());

console.log("UTC:", now.toUTCString());

Sample Output

Local: 22/6/2026, 4:45:18 PM

UTC: Mon, 22 Jun 2026 11:15:18 GMT

Another example:

Display the time in Japan.

const now = new Date();

console.log(
    now.toLocaleString("en-US", {
        timeZone: "Asia/Tokyo"
    })
);

Sample Output

6/22/2026, 8:15:18 PM

Automation Testing Example

Time zones are important when testing applications used across multiple countries.

Playwright Example

Verify a UTC timestamp returned by an application.

const timestamp = new Date().toISOString();

console.log(timestamp);

Sample Output

2026-06-22T11:15:18.456Z

Selenium Example

Compare local and UTC times.

const now = new Date();

console.log(now.toLocaleString());

console.log(now.toUTCString());

Cypress Example

Check the user’s local time zone.

const offset = new Date().getTimezoneOffset();

console.log(offset);

Sample Output

-330

API Testing Example

Validate an API timestamp.

const apiTime = new Date().toISOString();

console.log(apiTime);

Sample Output

2026-06-22T11:15:18.456Z

Data-Driven Testing Example

Generate a report using UTC time.

const reportTime = new Date().toUTCString();

console.log(reportTime);

Sample Output

Mon, 22 Jun 2026 11:15:18 GMT

Common Mistakes

Confusing Local Time with UTC

console.log(new Date().toLocaleString());

console.log(new Date().toISOString());

These methods produce different outputs because one uses the local time zone while the other uses UTC.

Assuming Everyone Has the Same Time Zone

Applications used worldwide must account for users in different time zones.

Avoid assuming all users share the same local time.

Ignoring Daylight Saving Time (DST)

Some countries adjust their clocks during part of the year.

JavaScript automatically applies Daylight Saving Time when the selected time zone observes it.

Best Practices

Store timestamps in UTC whenever possible.
Convert dates to the user’s local time before displaying them.
Use toISOString() for APIs and databases.
Use toLocaleString() for user-friendly displays.
Test applications with users in different time zones.
Be aware of Daylight Saving Time changes.
Avoid hardcoding time zone offsets.

Conclusion

Time zones are an important aspect of working with dates and times in JavaScript. The Date object provides built-in methods for working with both local time and UTC, making it easier to build applications that work correctly across different regions.

For automation engineers, understanding time zones is essential for validating timestamps, comparing server and client times, testing international applications, and ensuring consistent behavior across different geographic locations.

Mastering time zones helps you build reliable, globally accessible JavaScript applications.

Frequently Asked Questions (FAQs)