Intl.NumberFormat() constructor

locales Optional

A string with a BCP 47 language tag or an Intl.Locale instance, or an array of such locale identifiers. The runtime's default locale is used when undefined is passed or when none of the specified locale identifiers is supported. For the general form and interpretation of the locales argument, see the parameter description on the Intl main page.

The following Unicode extension key is allowed:

nu

See numberingSystem.

This key can also be set with options (as listed below). When both are set, the options property takes precedence.

options Optional

An object. For ease of reading, the property list is broken into sections based on their purposes, including locale options, style options, digit options, and other options.

Locale options

localeMatcher

The locale matching algorithm to use. Possible values are "lookup" and "best fit"; the default is "best fit". For information about this option, see Locale identification and negotiation.

numberingSystem

The numbering system to use for number formatting, such as "arab", "hans", "mathsans", and so on. For a list of supported numbering system types, see Intl.Locale.prototype.getNumberingSystems(). This option can also be set through the nu Unicode extension key; if both are provided, this options property takes precedence.

Style options

Depending on the style used, some of them may be ignored, and others may be required:

style

The formatting style to use.

"decimal" (default)

For plain number formatting.

"currency"

For currency formatting.

"percent"

For percent formatting.

"unit"

For unit formatting.

currency

The currency to use in currency formatting. Possible values are the ISO 4217 currency codes, such as "USD" for the US dollar, "EUR" for the euro, or "CNY" for the Chinese RMB — see the Current currency & funds code list. There is no default value; if the style is "currency", the currency property must be provided. It is normalized to uppercase.

currencyDisplay

How to display the currency in currency formatting.

"code"

Use the ISO currency code.

"symbol" (default)

Use a localized currency symbol such as €.

"narrowSymbol"

Use a narrow format symbol ("$100" rather than "US$100").

"name"

Use a localized currency name such as "dollar".

currencySign

In many locales, accounting format means to wrap the number with parentheses instead of appending a minus sign. Possible values are "standard" and "accounting"; the default is "standard".

unit

The unit to use in unit formatting, Possible values are core unit identifiers, defined in UTS #35, Part 2, Section 6. A subset of units from the full list was selected for use in ECMAScript. Pairs of simple units can be concatenated with "-per-" to make a compound unit. There is no default value; if the style is "unit", the unit property must be provided.

unitDisplay

The unit formatting style to use in unit formatting. Possible values are:

"short" (default)

E.g., 16 l.

"narrow"

E.g., 16l.

"long"

E.g., 16 litres.

Digit options

The following properties are also supported by Intl.PluralRules.

minimumIntegerDigits

The minimum number of integer digits to use. A value with a smaller number of integer digits than this number will be left-padded with zeros (to the specified length) when formatted. Possible values are from 1 to 21; the default is 1.

minimumFractionDigits

The minimum number of fraction digits to use. Possible values are from 0 to 100; the default for plain number and percent formatting is 0; the default for currency formatting is the number of minor unit digits provided by the ISO 4217 currency code list (2 if the list doesn't provide that information). See SignificantDigits/FractionDigits default values for when this default gets applied.

maximumFractionDigits

The maximum number of fraction digits to use. Possible values are from 0 to 100; the default for plain number formatting is the larger of minimumFractionDigits and 3; the default for currency formatting is the larger of minimumFractionDigits and the number of minor unit digits provided by the ISO 4217 currency code list (2 if the list doesn't provide that information); the default for percent formatting is the larger of minimumFractionDigits and 0. See SignificantDigits/FractionDigits default values for when this default gets applied.

minimumSignificantDigits

The minimum number of significant digits to use. Possible values are from 1 to 21; the default is 1. See SignificantDigits/FractionDigits default values for when this default gets applied.

maximumSignificantDigits

The maximum number of significant digits to use. Possible values are from 1 to 21; the default is 21. See SignificantDigits/FractionDigits default values for when this default gets applied.

roundingPriority

Specify how rounding conflicts will be resolved if both "FractionDigits" (minimumFractionDigits/maximumFractionDigits) and "SignificantDigits" (minimumSignificantDigits/maximumSignificantDigits) are specified. Possible values are:

"auto" (default)

The result from the significant digits property is used.

"morePrecision"

The result from the property that results in more precision is used.

"lessPrecision"

The result from the property that results in less precision is used.

The value "auto" is normalized to "morePrecision" if notation is "compact" and none of the four "FractionDigits"/"SignificantDigits" options are set.

Note that for values other than auto the result with more precision is calculated from the maximumSignificantDigits and maximumFractionDigits (minimum fractional and significant digit settings are ignored).

roundingIncrement

Indicates the increment at which rounding should take place relative to the calculated rounding magnitude. Possible values are 1, 2, 5, 10, 20, 25, 50, 100, 200, 250, 500, 1000, 2000, 2500, and 5000; the default is 1. It cannot be mixed with significant-digits rounding or any setting of roundingPriority other than auto.

roundingMode

How decimals should be rounded. Possible values are:

"ceil"

Round toward +∞. Positive values round up. Negative values round "more positive".

"floor"

Round toward -∞. Positive values round down. Negative values round "more negative".

"expand"

round away from 0. The magnitude of the value is always increased by rounding. Positive values round up. Negative values round "more negative".

"trunc"

Round toward 0. This magnitude of the value is always reduced by rounding. Positive values round down. Negative values round "less negative".

"halfCeil"

ties toward +∞. Values above the half-increment round like "ceil" (towards +∞), and below like "floor" (towards -∞). On the half-increment, values round like "ceil".

"halfFloor"

Ties toward -∞. Values above the half-increment round like "ceil" (towards +∞), and below like "floor" (towards -∞). On the half-increment, values round like "floor".

"halfExpand" (default)

Ties away from 0. Values above the half-increment round like "expand" (away from zero), and below like "trunc" (towards 0). On the half-increment, values round like "expand".

"halfTrunc"

Ties toward 0. Values above the half-increment round like "expand" (away from zero), and below like "trunc" (towards 0). On the half-increment, values round like "trunc".

"halfEven"

Ties towards the nearest even integer. Values above the half-increment round like "expand" (away from zero), and below like "trunc" (towards 0). On the half-increment values round towards the nearest even digit.

These options reflect the ICU user guide, where "expand" and "trunc" map to ICU "UP" and "DOWN", respectively. The rounding modes example below demonstrates how each mode works.

trailingZeroDisplay

The strategy for displaying trailing zeros on whole numbers. Possible values are:

"auto" (default)

Keep trailing zeros according to minimumFractionDigits and minimumSignificantDigits.

"stripIfInteger"

Remove the fraction digits if they are all zero. This is the same as "auto" if any of the fraction digits is non-zero.

SignificantDigits/FractionDigits default values

For the four options above (the FractionDigits and SignificantDigits options), we mentioned their defaults; however, these defaults are not unconditionally applied. They are only applied when the property is actually going to be used, which depends on the roundingPriority and notation settings. Specifically:

• If roundingPriority is not "auto", then all four options apply.
• If roundingPriority is "auto" and at least one SignificantDigits option is set, then the SignificantDigits options apply and the FractionDigits options are ignored.
• If roundingPriority is "auto", and either at least one FractionDigits option is set or notation is not "compact", then the FractionDigits options apply and the SignificantDigits options are ignored.
• If roundingPriority is "auto", notation is "compact", and none of the four options are set, then they are set to { minimumFractionDigits: 0, maximumFractionDigits: 0, minimumSignificantDigits: 1, maximumSignificantDigits: 2 }, regardless of the defaults mentioned above, and roundingPriority is set to "morePrecision".

Other options

notation

The formatting that should be displayed for the number. Possible values are:

"standard" (default)

Plain number formatting.

"scientific"

Return the order-of-magnitude for formatted number.

"engineering"

Return the exponent of ten when divisible by three.

"compact"

String representing exponent; defaults to using the "short" form.

compactDisplay

Only used when notation is "compact". Possible values are "short" and "long"; the default is "short".

useGrouping

Whether to use grouping separators, such as thousands separators or thousand/lakh/crore separators.

"always"

Display grouping separators even if the locale prefers otherwise.

"auto"

Display grouping separators based on the locale preference, which may also be dependent on the currency.

"min2"

Display grouping separators when there are at least 2 digits in a group.

true

Same as "always".

false

Display no grouping separators.

The default is "min2" if notation is "compact", and "auto" otherwise. The string values "true" and "false" are accepted, but are always converted to the default value.

signDisplay

When to display the sign for the number. Possible values are:

"auto" (default)

Sign display for negative numbers only, including negative zero.

"always"

Always display sign.

"exceptZero"

Sign display for positive and negative numbers, but not zero.

"negative"

Sign display for negative numbers only, excluding negative zero.

"never"

Never display sign.

A new Intl.NumberFormat object.

Normally, Intl.NumberFormat() can be called with or without new, and a new Intl.NumberFormat instance is returned in both cases. However, if the this value is an object that is instanceof Intl.NumberFormat (doesn't necessarily mean it's created via new Intl.NumberFormat; just that it has Intl.NumberFormat.prototype in its prototype chain), then the value of this is returned instead, with the newly created Intl.NumberFormat object hidden in a [Symbol(IntlLegacyConstructedSymbol)] property (a unique symbol that's reused between instances).

const formatter = Intl.NumberFormat.call(
  { __proto__: Intl.NumberFormat.prototype },
  "en-US",
  { notation: "scientific" },
);
console.log(Object.getOwnPropertyDescriptors(formatter));
// {
//   [Symbol(IntlLegacyConstructedSymbol)]: {
//     value: NumberFormat [Intl.NumberFormat] {},
//     writable: false,
//     enumerable: false,
//     configurable: false
//   }
// }

Note that there's only one actual Intl.NumberFormat instance here: the one hidden in [Symbol(IntlLegacyConstructedSymbol)]. Calling the format() and resolvedOptions() methods on formatter would correctly use the options stored in that instance, but calling all other methods (e.g. formatRange()) would fail with "TypeError: formatRange method called on incompatible Object", because those methods don't consult the hidden instance's options.

This behavior, called ChainNumberFormat, does not happen when Intl.NumberFormat() is called without new but with this set to anything else that's not an instanceof Intl.NumberFormat. If you call it directly as Intl.NumberFormat(), the this value is Intl, and a new Intl.NumberFormat instance is created normally.

RangeError

Thrown in one of the following cases:

• A property that takes enumerated values (such as style, units, currency, and so on) is set to an invalid value.
• Both maximumFractionDigits and minimumFractionDigits are set, and they are set to different values. Note that depending on various formatting options, these properties can have default values. It is therefore possible to get this error even if you only set one of the properties.

TypeError

Thrown if the options.style property is set to "unit" or "currency", and no value has been set for the corresponding property options.unit or options.currency.

In basic use without specifying a locale, a formatted string in the default locale and with default options is returned.

const amount = 3500;

console.log(new Intl.NumberFormat().format(amount));
// '3,500' if in US English locale

If the style is 'unit', a unit property must be provided. Optionally, unitDisplay controls the unit formatting.

const amount = 3500;

new Intl.NumberFormat("en-US", {
  style: "unit",
  unit: "liter",
}).format(amount); // '3,500 L'

new Intl.NumberFormat("en-US", {
  style: "unit",
  unit: "liter",
  unitDisplay: "long",
}).format(amount); // '3,500 liters'

If the style is 'currency', a currency property must be provided. Optionally, currencyDisplay and currencySign control the unit formatting.

const amount = -3500;
new Intl.NumberFormat("en-US", {
  style: "currency",
  currency: "USD",
}).format(amount); // '-$3,500.00'

new Intl.NumberFormat("bn", {
  style: "currency",
  currency: "USD",
  currencyDisplay: "name",
}).format(amount); // '-3,500.00 US dollars'

new Intl.NumberFormat("bn", {
  style: "currency",
  currency: "USD",
  currencySign: "accounting",
}).format(amount); // '($3,500.00)'

Scientific and compact notation are represented by the notation option and can be formatted like this:

new Intl.NumberFormat("en-US", {
  notation: "scientific",
}).format(987654321);
// 9.877E8

new Intl.NumberFormat("pt-PT", {
  notation: "scientific",
}).format(987654321);
// 9,877E8

new Intl.NumberFormat("en-GB", {
  notation: "engineering",
}).format(987654321);
// 987.654E6

new Intl.NumberFormat("de", {
  notation: "engineering",
}).format(987654321);
// 987,654E6

new Intl.NumberFormat("zh-CN", {
  notation: "compact",
}).format(987654321);
// 9.9亿

new Intl.NumberFormat("fr", {
  notation: "compact",
  compactDisplay: "long",
}).format(987654321);
// 988 millions

new Intl.NumberFormat("en-GB", {
  notation: "compact",
  compactDisplay: "short",
}).format(987654321);
// 988M

Display a sign for positive and negative numbers, but not zero:

new Intl.NumberFormat("en-US", {
  style: "percent",
  signDisplay: "exceptZero",
}).format(0.55);
// '+55%'

Note that when the currency sign is "accounting", parentheses might be used instead of a minus sign:

new Intl.NumberFormat("bn", {
  style: "currency",
  currency: "USD",
  currencySign: "accounting",
  signDisplay: "always",
}).format(-3500);
// '($3,500.00)'

You can specify the minimum or maximum number of fractional, integer or significant digits to display when formatting a number.

Using FractionDigits and IntegerDigits

The integer and fraction digit properties indicate the number of digits to display before and after the decimal point, respectively. If the value to display has fewer integer digits than specified, it will be left-padded with zeros to the expected number. If it has fewer fractional digits, it will be right-padded with zeros. Both cases are shown below:

// Formatting adds zeros to display minimum integers and fractions
console.log(
  new Intl.NumberFormat("en", {
    minimumIntegerDigits: 3,
    minimumFractionDigits: 4,
  }).format(4.33),
);
// "004.3300"

If a value has more fractional digits than the specified maximum number, it will be rounded. The way that it is rounded depends on the roundingMode property (more details are provided in the rounding modes section). Below the value is rounded from five fractional digits (4.33145) to two (4.33):

// Display value shortened to maximum number of digits
console.log(
  new Intl.NumberFormat("en", {
    maximumFractionDigits: 2,
  }).format(4.33145),
);
// "4.33"

The minimum fractional digits have no effect if the value already has more than 2 fractional digits:

// Minimum fractions have no effect if value is higher precision.
console.log(
  new Intl.NumberFormat("en", {
    minimumFractionDigits: 2,
  }).format(4.33145),
);
// "4.331"

The formatted value above is rounded to 3 digits, even though we didn't specify the maximum digits! This is because a default value of maximumFractionDigits is set when we specify minimumFractionDigits, and visa versa. The default values of maximumFractionDigits and minimumFractionDigits are 3 and 0, respectively.

You can use resolvedOptions() to inspect the formatter.

console.log(
  new Intl.NumberFormat("en", {
    maximumFractionDigits: 2,
  }).resolvedOptions(),
);
// {
//   …
//   minimumIntegerDigits: 1,
//   minimumFractionDigits: 0,
//   maximumFractionDigits: 2,
//   …
// }

console.log(
  new Intl.NumberFormat("en", {
    minimumFractionDigits: 2,
  }).resolvedOptions(),
);
// {
//   …
//   minimumIntegerDigits: 1,
//   minimumFractionDigits: 2,
//   maximumFractionDigits: 3,
//   …
// }

Using SignificantDigits

The number of significant digits is the total number of digits including both integer and fractional parts. The maximumSignificantDigits is used to indicate the total number of digits from the original value to display.

The examples below show how this works. Note in particular the last case: only the first digit is retained and the others are discarded/set to zero.

// Display 5 significant digits
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 5,
  }).format(54.33145),
);
// "54.331"

// Max 2 significant digits
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(54.33145),
);
// "54"

// Max 1 significant digits
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 1,
  }).format(54.33145),
);
// "50"

The minimumSignificantDigits ensures that at least the specified number of digits are displayed, adding zeros to the end of the value if needed.

// Minimum 10 significant digits
console.log(
  new Intl.NumberFormat("en", {
    minimumSignificantDigits: 10,
  }).format(54.33145),
);
// "54.33145000"

Specifying significant and fractional digits at the same time

The fraction digits (minimumFractionDigits/maximumFractionDigits) and significant digits (minimumSignificantDigits/maximumSignificantDigits) are both ways of controlling how many fractional and leading digits should be formatted. If both are used at the same time, it is possible for them to conflict.

These conflicts are resolved using the roundingPriority property. By default, this has a value of "auto", which means that if either minimumSignificantDigits or maximumSignificantDigits is specified, the fractional and integer digit properties will be ignored.

For example, the code below formats the value of 4.33145 with maximumFractionDigits: 3, and then maximumSignificantDigits: 2, and then both. The value with both is the one set with maximumSignificantDigits.

console.log(
  new Intl.NumberFormat("en", {
    maximumFractionDigits: 3,
  }).format(4.33145),
);
// "4.331"
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(4.33145),
);
// "4.3"
console.log(
  new Intl.NumberFormat("en", {
    maximumFractionDigits: 3,
    maximumSignificantDigits: 2,
  }).format(4.33145),
);
// "4.3"

Using resolvedOptions() to inspect the formatter, we can see that the returned object does not include maximumFractionDigits when maximumSignificantDigits or minimumSignificantDigits are specified.

console.log(
  new Intl.NumberFormat("en", {
    maximumFractionDigits: 3,
    maximumSignificantDigits: 2,
  }).resolvedOptions(),
);
// {
//   …
//   minimumIntegerDigits: 1,
//   minimumSignificantDigits: 1,
//   maximumSignificantDigits: 2,
//   …
// }
console.log(
  new Intl.NumberFormat("en", {
    maximumFractionDigits: 3,
    minimumSignificantDigits: 2,
  }).resolvedOptions(),
);
// {
//   …
//   minimumIntegerDigits: 1,
//   minimumSignificantDigits: 2,
//   maximumSignificantDigits: 21,
//   …
// }

In addition to "auto", you can resolve conflicts by specifying roundingPriority as "morePrecision" or "lessPrecision". The formatter calculates the precision using the values of maximumSignificantDigits and maximumFractionDigits.

The code below shows the format being selected for the three different rounding priorities:

const maxFracNF = new Intl.NumberFormat("en", {
  maximumFractionDigits: 3,
});
console.log(`maximumFractionDigits:3 - ${maxFracNF.format(1.23456)}`);
// "maximumFractionDigits:2 - 1.235"

const maxSigNS = new Intl.NumberFormat("en", {
  maximumSignificantDigits: 3,
});
console.log(`maximumSignificantDigits:3 - ${maxSigNS.format(1.23456)}`);
// "maximumSignificantDigits:3 - 1.23"

const bothAuto = new Intl.NumberFormat("en", {
  maximumSignificantDigits: 3,
  maximumFractionDigits: 3,
});
console.log(`auto - ${bothAuto.format(1.23456)}`);
// "auto - 1.23"

const bothLess = new Intl.NumberFormat("en", {
  roundingPriority: "lessPrecision",
  maximumSignificantDigits: 3,
  maximumFractionDigits: 3,
});
console.log(`lessPrecision - ${bothLess.format(1.23456)}`);
// "lessPrecision - 1.23"

const bothMore = new Intl.NumberFormat("en", {
  roundingPriority: "morePrecision",
  maximumSignificantDigits: 3,
  maximumFractionDigits: 3,
});
console.log(`morePrecision - ${bothMore.format(1.23456)}`);
// "morePrecision - 1.235"

Note that the algorithm can behave in an unintuitive way if a minimum value is specified without a maximum value. The example below formats the value 1 specifying minimumFractionDigits: 2 (formatting to 1.00) and minimumSignificantDigits: 2 (formatting to 1.0). Since 1.00 has more digits than 1.0, this should be the result when prioritizing morePrecision, but in fact the opposite is true:

const bothLess = new Intl.NumberFormat("en", {
  roundingPriority: "lessPrecision",
  minimumFractionDigits: 2,
  minimumSignificantDigits: 2,
});
console.log(`lessPrecision - ${bothLess.format(1)}`);
// "lessPrecision - 1.00"

const bothMore = new Intl.NumberFormat("en", {
  roundingPriority: "morePrecision",
  minimumFractionDigits: 2,
  minimumSignificantDigits: 2,
});
console.log(`morePrecision - ${bothMore.format(1)}`);
// "morePrecision - 1.0"

The reason for this is that only the "maximum precision" values are used for the calculation, and the default value of maximumSignificantDigits is much higher than maximumFractionDigits.

If a value has more fractional digits than allowed by the constructor options, the formatted value will be rounded to the specified number of fractional digits. The way in which the value is rounded depends on the roundingMode property.

Number formatters use halfExpand rounding by default, which rounds values "away from zero" at the half-increment (in other words, the magnitude of the value is rounded up).

For a positive number, if the fractional digits to be removed are closer to the next increment (or on the half way point) then the remaining fractional digits will be rounded up, otherwise they are rounded down. This is shown below: 2.23 rounded to two significant digits is truncated to 2.2 because 2.23 is less than the half increment 2.25, while values of 2.25 and greater are rounded up to 2.3:

// Value below half-increment: round down.
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(2.23),
);
// "2.2"

// Value on or above half-increment: round up.
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(2.25),
);
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(2.28),
);
// "2.3"
// "2.3"

A negative number on or below the half-increment point is also rounded away from zero (becomes more negative):

// Value below half-increment: round down.
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(-2.23),
);
// "-2.2"

// Value on or above half-increment: round up.
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(-2.25),
);
console.log(
  new Intl.NumberFormat("en", {
    maximumSignificantDigits: 2,
  }).format(-2.28),
);
// "-2.3"
// "-2.3"

The table below show the effect of different rounding modes for positive and negative values that are on and around the half-increment.

When using halfEven, its behavior also depends on the parity (odd or even) of the last digit of the rounded number. For example, the behavior of halfEven in the table above is the same as halfTrunc, because the magnitudes of all numbers are between a smaller "even" number (2.2) and a larger "odd" number (2.3). If the numbers are between ±2.3 and ±2.4, halfEven will behave like halfExpand instead. This behavior avoids consistently under- or over-estimating half-increments in a large data sample.

Sometimes we want to round the remaining fractional digits to some other increment than the next integer. For example, currencies for which the smallest coin is 5 cents might want to round the value to increments of 5, reflecting amounts that can actually be paid in cash.

This kind of rounding can be achieved with the roundingIncrement property.

For example, if maximumFractionDigits is 2 and roundingIncrement is 5, then the number is rounded to the nearest 0.05:

const nf = new Intl.NumberFormat("en-US", {
  style: "currency",
  currency: "USD",
  maximumFractionDigits: 2,
  roundingIncrement: 5,
});

console.log(nf.format(11.29)); // "$11.30"
console.log(nf.format(11.25)); // "$11.25"
console.log(nf.format(11.22)); // "$11.20"

This particular pattern is referred to as "nickel rounding", where nickel is the colloquial name for a USA 5 cent coin. To round to the nearest 10 cents ("dime rounding"), you could change roundingIncrement to 10.

const nf = new Intl.NumberFormat("en-US", {
  style: "currency",
  currency: "USD",
  maximumFractionDigits: 2,
  roundingIncrement: 5,
});

console.log(nf.format(11.29)); // "$11.30"
console.log(nf.format(11.25)); // "$11.25"
console.log(nf.format(11.22)); // "$11.20"

You can also use roundingMode to change the rounding algorithm. The example below shows how halfCeil rounding can be used to round the value "less positive" below the half-rounding increment and "more positive" if above or on the half-increment. The incremented digit is "0.05" so the half-increment is at .025 (below, this is shown at 11.225).

const nf = new Intl.NumberFormat("en-US", {
  style: "currency",
  currency: "USD",
  maximumFractionDigits: 2,
  roundingIncrement: 5,
  roundingMode: "halfCeil",
});

console.log(nf.format(11.21)); // "$11.20"
console.log(nf.format(11.22)); // "$11.20"
console.log(nf.format(11.224)); // "$11.20"
console.log(nf.format(11.225)); // "$11.25"
console.log(nf.format(11.23)); // "$11.25"

If you need to change the number of digits, remember that minimumFractionDigits and maximumFractionDigits must both be set to the same value, or a RangeError is thrown.

roundingIncrement cannot be mixed with significant-digits rounding or any setting of roundingPriority other than auto.

• Intl.NumberFormat
• Intl.supportedValuesOf()
• Intl