JavaScript Internationalization
Learn how to work with internationalization in JavaScript
Intl
is a powerful object that exposes the JavaScript Internationalization API.
It exposes the following properties:
Intl.Collator
: gives you access to language-sensitive string comparisonIntl.DateTimeFormat
: gives you access to language-sensitive date and time formattingIntl.NumberFormat
: gives you access to language-sensitive number formattingIntl.PluralRules
: gives you access to language-sensitive plural formatting and plural language rulesIntl.RelativeTimeFormat
: gives you access to language-sensitive relative time formatting
It also provides one method: Intl.getCanonicalLocales()
.
Intl.getCanonicalLocales()
lets you check if a locale is valid, and returns the correct formatting for it. It can accept a string, or an array:
Intl.getCanonicalLocales('it-it') //[ 'it-IT' ]
Intl.getCanonicalLocales(['en-us', 'en-gb']) //[ 'en-US', 'en-GB' ]
and throws an error if the locale is invalid
Intl.getCanonicalLocales('it_it') //RangeError: Invalid language tag: it_it
which you can catch with a try/catch block.
Different types can interface with the Intl API for their specific needs. In particular we can mention:
String.prototype.localeCompare()
Number.prototype.toLocaleString()
Date.prototype.toLocaleString()
Date.prototype.toLocaleDateString()
Date.prototype.toLocaleTimeString()
Let’s go and see how to work with the above Intl properties:
Intl.Collator
This property gives you access to language-sensitive string comparison
You initialize a Collator object using new Intl.Collator()
, passing it a locale, and you use its compare()
method which returns a positive value if the first argument comes after the second one. A negative if it’s the reverse, and zero if it’s the same value:
const collator = new Intl.Collator('it-IT')
collator.compare('a', 'c') //a negative value
collator.compare('c', 'b') //a positive value
We can use it to order arrays of characters, for example.
Intl.DateTimeFormat
This property gives you access to language-sensitive date and time formatting.
You initialize a DateTimeFormat object using new Intl.DateTimeFormat()
, passing it a locale, and then you pass it a date to format it as that locale prefers:
const date = new Date()
let dateTimeFormatter = new Intl.DateTimeFormat('it-IT')
dateTimeFormatter.format(date) //27/1/2019
dateTimeFormatter = new Intl.DateTimeFormat('en-GB')
dateTimeFormatter.format(date) //27/01/2019
dateTimeFormatter = new Intl.DateTimeFormat('en-US')
dateTimeFormatter.format(date) //1/27/2019
The formatToParts() method returns an array with all the date parts:
const date = new Date()
const dateTimeFormatter = new Intl.DateTimeFormat('en-US')
dateTimeFormatter.formatToParts(date)
/*
[ { type: 'month', value: '1' },
{ type: 'literal', value: '/' },
{ type: 'day', value: '27' },
{ type: 'literal', value: '/' },
{ type: 'year', value: '2019' } ]
*/
You can print the time as well. Check all the options you can use on MDN.
Intl.NumberFormat
This property gives you access to language-sensitive number formatting. You can use it to format a number as a currency value.
Say you have a number like 10
, and it represents the price of something.
You want to transform it to $10,00
.
If the number has more than 3 digits however it should be displayed differently, for example, 1000
should be displayed as $1.000,00
This is in USD, however.
Different countries have different conventions to display values.
JavaScript makes it very easy for us with the ECMAScript Internationalization API, a relatively recent browser API that provides a lot of internationalization features, like dates and time formatting.
It is very well supported:
const formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
})
formatter.format(1000) // "$1,000.00"
formatter.format(10) // "$10.00"
formatter.format(123233000) // "$123,233,000.00"
The minimumFractionDigits
property sets the fraction part to be always at least 2 digits. You can check which other parameters you can use in the NumberFormat MDN page.
This example creates a number formatter for the Euro currency, for the Italian country:
const formatter = new Intl.NumberFormat('it-IT', {
style: 'currency',
currency: 'EUR'
})
Intl.PluralRules
This property gives you access to language-sensitive plural formatting and plural language rules. I found the example on the Google Developers portal by Mathias Bynens the only one I could relate to practical usage: giving a suffix to ordered numbers: 0th, 1st, 2nd, 3rd, 4th, 5th..
const pr = new Intl.PluralRules('en-US', {
type: 'ordinal'
})
pr.select(0) //other
pr.select(1) //one
pr.select(2) //two
pr.select(3) //few
pr.select(4) //other
pr.select(10) //other
pr.select(22) //two
Every time we got other
, we translate that to th
. If we have one
, we use st
. For two
we use nd
. few
gets rd
.
We can use an object to create an associative array:
const suffixes = {
'one': 'st',
'two': 'nd',
'few': 'rd',
'other': 'th'
}
and we do a formatting function to reference the value in the object, and we return a string containing the original number, and its suffix:
const format = (number) => `${number}${suffixes[pr.select(number)]}`
Now we can use it like this:
format(0) //0th
format(1) //1st
format(2) //2nd
format(3) //3rd
format(4) //4th
format(21) //21st
format(22) //22nd
Note that there are nice things coming soon to Intl, like Intl.RelativeTimeFormat
and Intl.ListFormat
, which are at the time of writing only available in Chrome and Opera.
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