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How to format Date and Time strings with vanilla JavaScript

Today’s article is adapted from my new Vanilla JS Shorts on the Internationalization API.

Yesterday, we looked at how to get Date values with JavaScript. Today, we’re going to learn how to format date and time strings.

Let’s dig in!

The Intl.DateTimeFormat Object

The Intl.DateTimeFormat object can be used to format Date objects into a variety of string outputs. You can use the new Intl.DateTimeFormat() constructor to create a new Intl.DateTimeFormat object.

Pass in the locale to use, either as a string or array of strings.

There are a variety of acceptable formats for the locale:

  • A two-digit string. For example, en for English.
  • A tag and subtag. For example en-US for United States English or en-GB for Great Britain English.
  • Multiple subtags. For example, de-CH-1996 for the modern Swiss variant of German.

You can find a full list of tags and subtags on the IANA Language Subtag Registry.

// Create a new Intl.DateTimeFormat object
let formatter = new Intl.DateTimeFormat('en-US');

Formatting Options

The new Intl.DateTimeFormat() constructor also accepts an optional second argument, an object of options that define how the Date should be formatted.

You can mix-and-match them, or use none of them. If the dateStyle or timeStyle properties are defined, they can be used with each other but not with any other options.

// Define how the Date should be formatted
let formatter = new Intl.DateTimeFormat('en-US', {

	// The formatting style to use for the date
	// Can be used with timeStyle, but not with other options
	// 'full' (default), 'long', 'medium', 'short'
	dateStyle: 'full',

	// The formatting style to use for the time
	// Can be used with dateStyle, but not with other options
	// 'full' (default), 'long', 'medium', 'short'
	timeStyle: 'full',

	// If true, use 12-hour clock
	// Default is locale dependent
	hour12: true,

	// How to format the time of day (am, morning, etc.)
	// Only works if a 12-hour clock is used
	// 'narrow', 'short', or 'long'
	dayPeriod: 'narrow',

	// How to format the day of the week
	// 'long' ("Thursday"), 'short' ("Thu"), 'narrow' ("T")
	weekday: 'long',

	// How to format the era
	// 'long' ("Anno Domini"), 'short' ("AD"), 'narrow' ("A")
	era: 'short',

	// How to format the year
	// 'numeric' ("2023"), '2-digit' ("23")
	year: 'numeric',

	// How to format the month
	// 'numeric' ("3"), '2-digit' ("03"), 'long' ("March"), 'short' ("Mar"), 'narrow' ("M")
	month: 'long',

	// How to format the day of the month
	// 'numeric' ("1"), '2-digit' ("01")
	day: 'numeric',

	// How to format the hour of day
	// 'numeric', '2-digit'
	hour: 'numeric',

	// How to format the minutes
	// 'numeric', '2-digit'
	minute: 'numeric',

	// How to format the seconds
	// 'numeric', '2-digit'
	second: 'numeric',

	// Number of digits to include for fractions of second
	// 0 to 3
	fractionalSecondDigits: 0,

	// How to format the timezone
	// 'long' ("Eastern Standard Time"), 'short' ("EST"), 'shortOffset' ("GMT-5"), 'longOffset' ("GMT-0500"), 'shortGeneric' ("ET"), 'longGeneric' ("Eastern Time")
	timeZoneName: 'short'


Actually formatting the Date object into a string

Once you have an Intl.DateTimeFormat object with your formatting options defined, you can run the format() method on it, and pass in your Date object as an argument.

// Create an Intl.DateTimeFormat object
let formatter = new Intl.DateTimeFormat('en-US', {
	dateStyle: 'medium',
	timeStyle: 'short' 

// Create a Date object
let date = new Date('2023-10-31T22:00:00');

// Format a Date to a string
// returns "Oct 31, 2023, 10:00 PM"
let halloween = formatter.format(date);