How to format thousands with dot and decimal with comma

Question

How can I format thousands with dot and decimal with comma?

Input: 3197769.7000000007

Expected: 3.197.769,7000000007

I tried the following regex, but it doesn't feel clean enough. I feel like answer should be similar to How to format a number with commas as thousands separators?, 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, '.'));

@adiga for those marking as duplicate. please notice regex tag — Shinjo, Dec 06 '22 at 09:35
It is also marked with javascript and there are native ways to do this than complicated regex — adiga, Dec 06 '22 at 09:36
@Shinjo Not everything needs to be solved with regular expressions. And not everything _should_ or even _can_ be solved with regular expressions. — Sebastian Simon, Dec 06 '22 at 09:36
In most cases one would use the formatting of [`Intl.NumberFormat`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat/NumberFormat) ... `console.log(new Intl.NumberFormat('de-DE', { maximumFractionDigits: 10 }).format('3197769.7000000007'));` — Peter Seliger, Dec 06 '22 at 10:37
You have an [xy problem](https://xyproblem.info/) :). A regex is the wrong tool for formatting a number. — AD7six, Dec 06 '22 at 11:08
I agree that regex is not the best suited tool since the [Internationalization Web API](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl) 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 ... [`String(3197769.7000000007).replace('.', ',').replace(/\d(?=(?:(?:\d{3})+),)/g, match => \`${ match }.\`);`](https://regex101.com/r/3pvKHl/1) — Peter Seliger, Dec 06 '22 at 11:41

score 2 · Answer 1 · answered Dec 06 '22 at 12:40

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.

Thanks, it works fine for the most part, except when it doesn't have a decimal, it fails to [separate thousands](https://i.stack.imgur.com/rbZjd.png). — Shinjo, Dec 07 '22 at 02:48

How to format thousands with dot and decimal with comma

1 Answers1