Intl.NumberFormat.prototype.formatToParts()

The formatToParts() method of Intl.NumberFormat instances allows locale-aware formatting of strings produced by this Intl.NumberFormat object.

Syntax

formatToParts()
formatToParts(number)

Parameters

number
- : A Number or BigInt to format.

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:

compact
- : The exponent in "long" or "short" form, depending on how compactDisplay (which defaults to short) is specified when notation is set to compact.
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 (".").
exponentInteger
- : The exponent integer value, when notation is set to scientific or engineering.
exponentMinusSign
- : The exponent minus sign string ("-").
exponentSeparator
- : The exponent separator, when notation is set to scientific or engineering.
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 ("%").
unit
- : The unit string, such as the "l" or "litres", depending on how unitDisplay is specified.
unknown
- : The string for unknown type results.

Examples

Comparing format and formatToParts

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

const number = 3500;

const 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.

const numberString = formatter
  .formatToParts(number)
  .map(({ type, value }) => {
    switch (type) {
      case "currency":
        return `<strong>${value}</strong>`;
      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 <strong>€</strong>"

Syntax

Parameters

Return value

Description

Examples

Comparing format and formatToParts

Specifications

Browser compatibility

See also