Intl.NumberFormat.prototype.format()

number

A Number or BigInt to format.

The format getter function formats a number into a string according to the locale and formatting options of this Intl.NumberFormat object.

Use the format getter function for formatting a single currency value, here for Russia:

var options = { style: 'currency', currency: 'RUB' };
var numberFormat = new Intl.NumberFormat('ru-RU', options);
console.log(numberFormat.format(654321.987));
// → "654 321,99 руб."

Use the format getter function for formatting all numbers in an array. Note that the function is bound to the Intl.NumberFormat from which it was obtained, so it can be passed directly to Array.prototype.map. This is considered a historical artefact, as part of a convention which is no longer followed for new features, but is preserved to maintain compatibility with existing programs.

var a = [123456.789, 987654.321, 456789.123];
var numberFormat = new Intl.NumberFormat('es-ES');
var formatted = a.map(n => numberFormat.format(n));
console.log(formatted.join('; '));
// → "123.456,789; 987.654,321; 456.789,123"

• Intl.NumberFormat
• Number.prototype.toLocaleString()