Intl.DateTimeFormat.prototype.formatToParts()

The Intl.DateTimeFormat.prototype.formatToParts() method allows locale-aware formatting of strings produced by DateTimeFormat formatters.

Syntax

Intl.DateTimeFormat.prototype.formatToParts(date)

Parameters

date Optional

The date to format.

Return value

An Array of objects containing the formatted date in parts.

Description

The formatToParts() method is useful for custom formatting of date strings. It returns an Array of objects containing the locale-specific tokens from which it possible to build custom strings while preserving the locale-specific parts. The structure the formatToParts() method returns, looks like this:

[
  { type: "day", value: "17" },
  { type: "weekday", value "Monday" }
]

Possible types are the following:

day

The string used for the day, for example "17".

dayPeriod

The string used for the day period, for example, "AM" or "PM".

era

The string used for the era, for example "BC" or "AD".

hour

The string used for the hour, for example "3" or "03".

literal

The string used for separating date and time values, for example one of " : , / ".

minute

The string used for the minute, for example "00".

month

The string used for the month, for example "12".

second

The string used for the second, for example "07" or "42".

timeZoneName

The string used for the name of the time zone, for example "UTC".

weekday

The string used for the weekday, for example "M", "Monday", or "Montag".

year

The string used for the year, for example "2012" or "96".

Examples

DateTimeFormat outputs localized, opaque strings that cannot be manipulated directly:

var date = Date.UTC(2012, 11, 17, 3, 0, 42);

var formatter = new Intl.DateTimeFormat("en-us", {
  weekday: 'long',
  year: 'numeric',
  month: 'numeric',
  day: 'numeric',
  hour: 'numeric',
  minute: 'numeric',
  second: 'numeric',
  hour12: true,
  timeZone: "UTC"
});

formatter.format(date);
// "Monday, 12/17/2012, 3:00:42 AM"

However, in many User Interfaces there is a desire to customize the formatting of this string. The formatToParts method enables locale-aware formatting of strings produced by DateTimeFormat formatters by providing you the string in parts:

formatter.formatToParts(date);

// return value: 
[ 
  { type: 'weekday',   value: 'Monday' }, 
  { type: 'literal',   value: ', '     }, 
  { type: 'month',     value: '12'     }, 
  { type: 'literal',   value: '/'      }, 
  { type: 'day',       value: '17'     }, 
  { type: 'literal',   value: '/'      }, 
  { type: 'year',      value: '2012'   }, 
  { type: 'literal',   value: ', '     }, 
  { type: 'hour',      value: '3'      }, 
  { type: 'literal',   value: ':'      }, 
  { type: 'minute',    value: '00'     }, 
  { type: 'literal',   value: ':'      }, 
  { type: 'second',    value: '42'     }, 
  { type: 'literal',   value: ' '      }, 
  { type: 'dayPeriod', value: 'AM'     } 
]

Now the information is available separately and it can be formatted and concatenated again in a customized way. For example by using Array.prototype.map(), arrow functions, a switch statement, template literals, and Array.prototype.reduce().

var dateString = formatter.formatToParts(date).map(({type, value}) => { 
  switch (type) {
    case 'dayPeriod': return `<strong>${value}</strong>`; 
    default : return value; 
  } 
}).reduce((string, part) => string + part);

This will make the day period bold, when using the formatToParts() method.

console.log(formatter.format(date));
// "Monday, 12/17/2012, 3:00:42 AM"

console.log(dateString);
// "Monday, 12/17/2012, 3:00:42 <strong>AM</strong>"

Polyfill

A polyfill for this feature is available in the proposal repository.

Specifications

Browser compatibility

[1] This method is implemented since Chrome 55 behind the --datetime-format-to-parts command line parameter (see V8 issue 5244).

[2] This method was implemented in Gecko 51 (Firefox 51.0 / Thunderbird 51.0 / SeaMonkey 2.48) (see bug 1216150).

[3] This method was initially only exposed to B2G system apps starting from Gecko 46 (Firefox 46.0 / Thunderbird 46.0 / SeaMonkey 2.43) (see bug 1216150). In Gecko 51 (Firefox 51.0 / Thunderbird 51.0 / SeaMonkey 2.48) it was exposed to web content (see bug 1289340).

See also

• Intl.DateTimeFormat
• Intl.DateTimeFormat.prototype.format
• Date.prototype.toLocaleString()
• Date.prototype.toLocaleDateString()
• Date.prototype.toLocaleTimeString()