JS Intl.DateTimeFormat formatToParts()
The Intl.DateTimeFormat.prototype.formatToParts() method allows locale-aware formatting of strings produced by DateTimeFormat formatters.
Syntax
dateTimeFormat.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 "/", ",", "o'clock", "de", etc.
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 `${value}`;
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 AM"
Polyfill
A polyfill for this feature is available in the proposal repository.
Specifications
| Specification | Status | Comment |
|---|---|---|
| [ECMAScript Internationalization API 4.0 (ECMA-402) | ||
| The definition of ‘Intl.DateTimeFormat.prototype.formatToParts’ in that specification.](https://tc39.es/ecma402/#sec-Intl.DateTimeFormat.prototype.formatToParts) | Draft | Initial definition |
