JS Intl.NumberFormat formatToParts()
The Intl.Numberformat.prototype.formatToParts() method allows locale-aware formatting of strings produced by NumberTimeFormat formatters.
Syntax
Intl.NumberFormat.prototype.formatToParts(number)
Parameters
number Optional
Return value
An Array of objects containing the formatted number in parts.
Description
The formatToParts() method is useful for custom formatting of number 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: "integer", value: "3" }
{ type: "group", value: "." }
{ type: "integer", value: "500" }
]
Possible types are the following:
currency
The currency string, such as the symbols “$” and “€” or the name “Dollar”, “Euro” depending on how currencyDisplay is specified.
decimal
The decimal separator string (".").
fraction
The fraction number.
group
The group separator string (",").
infinity
The Infinity string (“∞”).
integer
The integer number.
literal
Any literal strings or whitespace in the formatted number.
minusSign
The minus sign string ("-").
nan
The NaN string (“NaN”).
plusSign
The plus sign string ("+").
percentSign
The percent sign string ("%").
Examples
NumberFormat outputs localized, opaque strings that cannot be manipulated directly:
var number = 3500;
var formatter = new Intl.NumberFormat('de-DE', {
style: 'currency',
currency: 'EUR'
});
formatter.format(number);
// "3.500,00 €"
However, in many User Interfaces there is a desire to customize the formatting of this string. The formatToParts method enables locale-aware formatting of strings produced by NumberFormat formatters by providing you the string in parts:
formatter.formatToParts(number);
// return value:
[
{ type: "integer", value: "3" }
{ type: "group", value: "." }
{ type: "integer", value: "500" }
{ type: "decimal", value: "," }
{ type: "fraction", value: "00" }
{ type: "literal", value: " " }
{ type: "currency", value: "€" }
]
Now the information is available separately and it can be formatted and concatenated again in a customized way. For example by using Array.prototype.map(), [arrow functions], a [switch statement], template literals, and Array.prototype.reduce().
var numberString = formatter.formatToParts(number).map(({type, value}) => {
switch (type) {
case 'currency': return `${value}`;
default : return value;
}
}).reduce((string, part) => string + part);
This will make the currency bold, when using the formatToParts() method.
console.log(numberString);
// "3.500,00 €"
Polyfill
A polyfill for this feature is available in the proposal repository.
