A currency-aware way to set minimumFractionDigits

When displaying currencies in our app, we more or less always want to show 2 decimal points, for cents on all numbers. We can do this with formatNumber by modifying the minimumFractionDigits attribute. This works well, but there are certain currencies that we don’t want decimal points on. Namely, currencies whose base unit is also its smallest unit, like the Yen (and about 13 other currencies).

I actually think this might be a bad “feature” to add to the helper, but maybe some good advice/documentation on how to achieve this would be helpful to others.

My gut says there’s a way to “reopen” the helper somewhere in my app, and force defaults for minimumFractionDigits if they aren’t explicitly set. Then I can do the work to know when to set and what to set those defaults to.

Make sense? Can you think of any pretty way to do this?

Here’s my relevant code from my programmatic wrapper of NumberFormat, just to give perspective on what I’m doing.

// some setup

const non100UnitDenominators = {
  bif: 1, // Burundian Franc
  clp: 1, // Chilean Peso
  djf: 1, // Djiboutian Franc
  gnf: 1, // Guinean Franc
  jpy: 1, // Japanese Yen
  kmf: 1, // Comorian Franc
  krw: 1, // South Korean Won
  mga: 1, // Malagasy Ariary
  pyg: 1, // Paraguayan Guaraní
  rwf: 1, // Rwandan Franc
  vnd: 1, // Vietnamese Đồng
  vuv: 1, // Vanuatu Vatu
  xaf: 1, // Central African Cfa Franc
  xof: 1, // West African Cfa Franc
  xpf: 1, // Cfp Franc
};

function getUnitDenominator(currency) {
  currency = currency.toLowerCase();
  return non100UnitDenominators[currency] || 100;
}

And in the actual file.

  if (options.style === 'currency') {
    // If we have a 'common' currency, which comes in 'cents', force 2 decimal points
    if (getUnitDenominator(options.currency) === 100) {
      if (typeof options.minimumFractionDigits === 'undefined') {
        options.minimumFractionDigits = 2;
      }
      if (typeof options.maximumFractionDigits === 'undefined') {
        options.maximumFractionDigits = 2;
      }
    }
  }

Would love your opinions!

[jelhan]

Since it was mentioned before I tested rounding having maximumFractionDigits set and result was as expected - at least in Internet Explorer 11, Chrome and Firefox.

I did not test Safari or any mobile browsers behaviour yet. So can’t say if it’s only Chrome and related browsers which behave strange.

[stale[bot]]

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