How to format thousands with dot and decimal with comma?

Input: 3197769.7000000007

Expected: 3.197.769,7000000007

Tried the following regex but doesn't feel clean enough. I feel like answer should be similar to https://stackoverflow.com/a/2901298/11328122 but I don't have enough regex knowledge for it.

const value = 3197769.7000000007
console.log(value.toString().replace(/\B(?<!\.\d*)(?=(\d{3}) (?!\d))/g, "#").replace('.', ',').replace(/#/g, '.'));

CodePudding user response：

You can use the Intl.NumberFormat method to format numbers:

const value = 3197769.7000000007;
const formatter = new Intl.NumberFormat('de-DE', {
  style: 'decimal',
  useGrouping: true,
  maximumFractionDigits: 20
});
// Output: 3.197.769,7000000007
console.log(formatter.format(value));

CodePudding user response：

I agree that regex is not the best suited tool since the Internationalization Web API offers safer and more convenient solutions. Anyhow what I see from the OP's used regex and also from the linked thread, I have to say that there are much cleaner and more straightforward regex and replace based solutions like e.g. this one ...

console.log(
  '3197769.7000000007 =>',

  String(3197769.7000000007)

    // - replace the standard decimal separator by a comma.
    .replace('.', ',')

    // - see ... [https://regex101.com/r/3pvKHl/1]
    // - replace every digit which is followed
    //   by a sequence of 3-digit groups/blocks
    //   until the comma by the very digit itself
    //   and the thousands block separating dot.
    .replace(/\d(?=(?:(?:\d{3}) ),)/g, match => `${ match }.`)
);
console.log(
  '6291563197769.587 =>',

  String(6291563197769.587)
    .replace('.', ',')
    .replace(/\d(?=(?:(?:\d{3}) ),)/g, match => `${ match }.`)
);

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

... where one would

• e.g. cast the number into a string value via the String function,

• replace the sole occurrence of the decimal delimiter (dot) by a comma,

• replace every digit which is followed by a sequence of 3-digit groups/blocks until the comma by the very digit itself and the thousands block separating dot ...

  • ... with the help of following regex ... /\d(?=(?:(?:\d{3}) ),)/g where the regex reads as follows ...

    • / \d (?= (?:(?:\d{3}) ), ) /g ... globally match a single digit/\d followed by a lookahead/(?= ... ) where the pattern of the lookahead

    • (?:(?:\d{3}) ) , ... enforces a comma which is headed by at least a single block of exactly 3 digits/\d{3} which also is allowed to become a sequence of blocks of always 3 digits each/(?:\d{3}) .

    • Note ... the pattern (?: ... ) is used for grouping where the matching expression is meant to not be captured.