Does JavaScript take local decimal separators into account?

Question

I\'ve got a web page that displays decimals in a user\'s localized format, like so:

• English: 7.75
• Dutch: 7,75

Answer 1

Expanding on the solution from @naitsirch we can use Intl.NumberFormat.formatToParts() to have JS parse the group and decimal separators.

function parseLocaleNumber(stringNumber) {
  let num = 123456.789,
    fmt_local = new Intl.NumberFormat(),
    parts_local = fmt_local.formatToParts(num),
    group = '',
    decimal = '';

  parts_local.forEach(function(i) {
    switch (i.type) {
      case 'group':
        group = i.value;
        break;
      case 'decimal':
        decimal = i.value;
        break;
      default:
        break;
    }
  });

  return parseFloat(stringNumber
    .replace(new RegExp('\\' + group, 'g'), '')
    .replace(new RegExp('\\' + decimal), '.')
  );
}

//replace this string with a number formatted for your locale
console.log(parseLocaleNumber("987,654,321.01"));
//output for "en" locale: 987654321.01

Answer 2

No, decimal separators are not localized at all in JavaScript, and parseFloat() parses numbers in the same format as you need to use in JavaScript source code: “.” as decimal separator, no group (thousands) separator, “E” or “e” as “times ten to power” symbol, and Ascii hyphen “-” as minus sign.

To read or write numbers in localized format, you need something else. I would recommend the Globalize.js library, unless you can limit yourself to the single issue of decimal separator and a limited number of languages—in that case, it might be simpler to do just string manipulation that maps “.” to “,” on output and vice versa on input.

Answer 3

No, comma (,) is an operator having special meaning, just like dot (.). Otherwise things as simple as:

var array1 = [1,2];
var array2 = [1.2];

would break under different locales. All mainstream languages I know treat . and , separately and stricly, irrespective to locale.

Answer 4

No, the separator is always a dot (.) in a javascript Number. So 7,75 evaluates to 75, because a , invokes left to right evaluation (try it in a console: x=1,x+=1,alert(x), or more to the point var x=(7,75); alert(x);). If you want to convert a Dutch (well, not only Dutch, let's say Continental European) formatted value, it should be a String. You could write an extension to the String prototype, something like:

String.prototype.toFloat = function(){
      return parseFloat(this.replace(/,(\d+)$/,'.$1'));
};
//usage
'7,75'.toFloat()+'7,75'.toFloat(); //=> 15.5

Note, if the browser supports it you can use Number.toLocaleString

console.log((3.32).toLocaleString("nl-NL"));
console.log((3.32).toLocaleString("en-UK"));

.as-console-wrapper { top: 0; max-height: 100% !important; }

Answer 5

Here's an example for a locale aware number parser:

function parseLocaleNumber(stringNumber) {
    var thousandSeparator = (1111).toLocaleString().replace(/1/g, '');
    var decimalSeparator = (1.1).toLocaleString().replace(/1/g, '');

    return parseFloat(stringNumber
        .replace(new RegExp('\\' + thousandSeparator, 'g'), '')
        .replace(new RegExp('\\' + decimalSeparator), '.')
    );
}

It uses the current locale of the browser to replace thousand and decimal separators.

With a German locale setting

var n = parseLocaleNumber('1.000.045,22');

n will be equal to 1000045.22.

Answer 6

Taking the symbol into account, this works in all cases:

parseLocaleNumber: function ( stringNumber ) 
{
    let thousandSeparator = (11111).toLocaleString().replace(/1/g, '');
    let decimalSeparator = (1.1).toLocaleString().replace(/1/g, '');
    let symbol = (0).toLocaleString()
        .replace(/0/g, '')
        .replace(new RegExp('\\' + decimalSeparator), '.')
        .trim();

    return parseFloat(
        stringNumber
            .replace(new RegExp('\\' + thousandSeparator, 'g'), '')
            .replace(new RegExp('\\' + decimalSeparator), '.')
            .replace(new RegExp( symbol ), '')
    );
}

2 details highlighted:

1. use 11111 instead of 1111 because the first always shows thousand separator by default.
2. Number format always uses '.' as decimal separator