Agnostic, extensible and composable set of functions for formatting numbers to currency

currencyFormatter.js

// :: delimitGroups = (number, string) => string => string
const delimitGroups = (groupSize, delimiter) => s =>
  s.split('')
   .reduceRight((acc, x, i) =>
      `${x}${(s.length - 1 - i) % groupSize ? '' : delimiter}${acc}`)

// :: format = number => object => string
export const format = options => n =>
  (([left, right]) =>
    `${options.symbol}${
       delimitGroups(options.groupSize, options.groupSeparator)(left)
     }${options.decimalSeparator}${right}`
  )(n.toFixed(options.decimals).split('.'))

// :: formatWithOptions = object => (number, object) => string
export const formatWithOptions = options => (n, overrides = {}) =>
  format({
    ...options,
    ...overrides
  })(n)

// USAGE

// configs

const currencyLocale = {
  NZD: {
    symbol: '$',
    groupSize: 3, 
    groupSeparator: ',', 
    decimalSeparator: '.',
    decimals: 2
  },
  BRL: {
    symbol: 'R$',
    groupSize: 3, 
    groupSeparator: '.', 
    decimalSeparator: ',',
    decimals: 2
  }
}

// high level localized wrappers

const formatNZD = formatCurrencyWithOptions(currencyLocale.NZD)
const formatBRL = formatCurrencyWithOptions(currencyLocale.BRL)

console.log(
  formatNZD(2.32), // $2.32
  formatNZD(11231232.324567, { decimals: 4, symbol: '' }), // 11,231,232.3246
  formatBRL(32135.35267) // R$32.135,35
)