Time Formats on the Web

This interactive page explains everything about time formats, time zones, and how JavaScript deals with date and time. You’ll see live examples as you change the date, time, and selected time zone.

1. Input a Date and Time

Use the control below to pick a date and time. The browser will display a localized picker.

2. Select a Time Zone

Choose a time zone to see how the same moment is represented in different parts of the world.

Deep Dive: Concepts Behind the Code

Time Formats

Time formats determine how date and time information is structured and communicated:

  • ISO 8601: An internationally accepted way to represent date and time (e.g. 2025-03-06T12:00:00Z). It’s the standard output for many APIs.
  • RFC 2822: Often used in email headers, formatted like Thu, 06 Mar 2025 12:00:00 +0000.
  • Unix Timestamp: A numeric representation (milliseconds since January 1, 1970) that is often used in computing.

JavaScript provides methods like toISOString(), toUTCString(), and toString() to convert date objects into these formats.

Time Zones

Time zones help us interpret a moment in time according to geographical and political regions:

  • UTC (Coordinated Universal Time): The baseline time zone from which all others are calculated.
  • Local Time: The time as configured on the user’s device, which may adjust for daylight saving.
  • IANA Time Zone Database: A comprehensive database that JavaScript’s Intl API leverages to format dates in specific regions.

For advanced handling, libraries like Moment Timezone or Luxon provide even greater control.

JavaScript and Time Handling

The built-in Date object in JavaScript, along with the modern Intl API, provides tools to:

  • Create Dates: Using new Date() to generate a date object from a variety of inputs.
  • Parse Strings: Converting a date string into a Date object using Date.parse().
  • Format Dates: With methods such as toISOString(), toUTCString(), and toString().

As you build more complex applications, consider using libraries that add more power and clarity when handling internationalization and time zones.

Additional Resources