Guide to Parsing Numbers from Any Locale

As an example locale, I’m using ar-DZ-u-nu-arab (an arabic locale with an arabic numbering system). This number format does not share anything in common with U.S. english.

The following number is what we will be parsing:

const localizedString = '-١٬٢٣٤٫٥٦'; // will result in -1234.56

Replacing the group and decimal symbols

First we need to determine the group and decimal symbols of the locale, by formatting a test number:

const parts = new Intl.NumberFormat('ar-DZ-u-nu-arab').formatToParts(1111.11);
const groupSymbol = parts.find((d) => d.type === 'group').value; // ٫
const decimalSymbol = parts.find((d) => d.type === 'decimal').value; // ٬

Now that we know the symbols used by the locale, we can remove the grouping symbols and replace the decimal symbol with a period.

localizedString.replace(new Regex(groupSymbol, 'g'), '').replace(decimalSymbol, '.'); // -١٢٣٤.٥٦

Replacing the numerals

Now we need to determine the numerals used in the locale. We do this by formatting all digits, and ordering them from 0 to 9 so that the index equals the digit.

const numerals = new Intl.NumberFormat('ar-DZ-u-nu-arab', {useGrouping: false})
.format(9876543210).split('').reverse().join(''); // ٠١٢٣٤٥٦٧٨٩

Now we create a regular expression with the numbers:

const numeralRegex = new RegExp(`[${numerals}]`, 'g');

Now we can replace the digits with the standard 0-9 digits:

.replace(numeralRegex, (group: string) => {
  return numerals.indexOf(group).toString();
}); // -1234.56

Final steps

We want to allow the use of either minus sign character (remember that some locales use a different character for the minus sign):

.replace(/[−-]\s?/, '-') // -1234.56

Finally, we can parse to a Number. After this step, any invalid values will be NaN.

Number(...) // -1234.56

Putting it altogether

Here is what a reusable class might look like:

export class NumberParser {
  private groupSymbol: string;
  private decimalSymbol: string;
  private numerals;
  private numeralRegex;

  constructor(private readonly locale: string) {
    const parts = Intl.NumberFormat(locale).formatToParts(1111.11);
    this.groupSymbol = parts.find(part => part.type === 'group').value;
    this.decimalSymbol = parts.find(part => part.type === 'decimal').value;
    this.numerals = new Intl.NumberFormat(locale, {useGrouping: false}).format(9876543210).split('').reverse().join('');
    this.numeralRegex = new RegExp(`[${this.numerals}]`, 'g');
  }

  parse(localizedNumber: string): number {
    if (!localizedNumber) {
      return null;
    }
    return Number(
      localizedNumber.replace(new Regex(this.groupSymbol, 'g'), '')
      .replace(this.decimalSymbol, '.')
      .replace(/[−-]\s?/, '-')
      .replace(this.numeralRegex, (group: string) => {
        return this.numerals.indexOf(group).toString();
      })
    );
  }
}

Number inputs in any locale

If you need to allow number inputs to work with any locale, you need to use <input type="text"/>, since the localized number can contain symbols that are not allowed in <input type="number"/>.

Then, whenever the user changes the number, you need to parse the localized string back to a javascript number, so it can be sent to the server in the right format.

React Example

Here is an example of a number input component in react:

export default function NumberInput({locale, initialValue}) {
  const [localeValue, setLocaleValue] = useState(new Intl.NumberFormat(locale).format(initialValue));
  const [numberValue, setNumberValue] = useState(initialValue);
  const parser = new NumberParser(locale);

  const handleChange = (e) => {
    setLocaleValue(e.target.value);
    setNumberValue(parser.parse(e.target.value));
  };
  return (
    <div>
      <input type="text" value={localeValue} onChange={handleChange}/>
      <div>Number value: {numberValue}</div>
    </div>
  );
}

The localeValue (type string) is what we want to use for the input field. And the numberValue (type number) is what we use for the system value (the value we get and send from the server).

Localizing a number input in angular

I published a NPM package for angular called ngx-decimal: https://www.npmjs.com/package/ngx-decimal

It handles everything for you. Example usage is:

<input type="text" ngxDecimal [(ngModel)]="numberValue">

Number Localization

Parsing Guide