Currency Formatting with Intl.NumberFormat and Locale-Aware Display

Displaying prices correctly across locales requires knowledge of symbol position, decimal separators, and currency codes that vary by region.

Use Intl.NumberFormat with style: 'currency' and the appropriate ISO 4217 currency code. The locale controls symbol position and decimal convention.

function formatCurrency(amount, currency, locale) {
  return new Intl.NumberFormat(locale, {
    style: 'currency',
    currency,
    minimumFractionDigits: 2,
    maximumFractionDigits: 2,
  }).format(amount);
}

formatCurrency(1234.5, 'USD', 'en-US') // '$1,234.50'
formatCurrency(1234.5, 'USD', 'de-DE') // '1.234,50 
formatCurrency(1234.5, 'EUR', 'fr-FR') // '1\u202f234,50 \u20ac'
formatCurrency(1234.5, 'JPY', 'ja-JP') // '\uffe51,235' (no decimals)

// narrowSymbol for compact display
new Intl.NumberFormat('en-US', {
  style: 'currency',
  currency: 'USD',
  currencyDisplay: 'narrowSymbol', // ' not 'US
}).format(1234.5)

Currency display conventions differ: the US puts $ before the number, Germany puts it after, France uses a non-breaking space before the symbol. The Intl API handles all of this via CLDR data.