Regex Javascript add space after punctuation

Question

Currently I'm using replace(/\s*([,.!?:;])[,.!?:;]*\s*/g, '$1 ') to add space after punctuation. But it doesn't work if the sentence contains three dots.

Example text: "Hello,today is a beautiful day...But tomorrow is,not."

Expected output: "Hello, today is a beautiful day... But tomorrow is, not."

let text = "Hello,today is a beautiful day...But tomorrow is,not.";
text = text.replace(/\s*([,.!?:;])[,.!?:;]*\s*/g, '$1 ')

Gives: "Hello, today is a beautiful day. But tomorrow is, not. "

Please tell me what regex I can use so that I can get the expected output.

Why do you remove all consecutive punctuation but the first one? Try just /\s*([,.!?:;]+)\s*/g. See regex101.com/r/mKgPFG/1 — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 17, 2020 at 12:35
Do you want to catch the last (sequence) of punctuation too? This would add a space at the end of a line. Maybe use some trim function right after, or add to the pattern itself. — JvdV
– JvdV, Commented Nov 17, 2020 at 12:37
Yeah, adding that condition to the above regex is simple: /\s*([,.!?:;]+)(?!\s*$)\s*/g. Please explain your regex requirements in detail. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 17, 2020 at 12:39

Wiktor Stribiżew · Accepted Answer · 2020-11-17 13:02:55Z

6

You should match all consecutive punctuation chars into Group 1, not just the first char. Also, it makes sense to exclude a match of the punctuation at the end of the string.

You can use

text.replace(/\s*([,.!?:;]+)(?!\s*$)\s*/g, '$1 ')

Also, it still might be handy to .trim() the result. See the regex demo.

Details

\s* - 0 or more whitspace chars
([,.!?:;]+) - Group 1 ($1): one or more ,, ., !, ?, : or ;
(?!\s*$) - if not immediately followed with zero or more whitespace chars and then end of string
\s* - 0 or more whitspace chars

See a JavaScript demo:

let text = "Hello,today is a beautiful day...But tomorrow is,not.";
text = text.replace(/\s*([,.!?:;]+)(?!\s*$)\s*/g, '$1 ');
console.log(text);

answered Nov 17, 2020 at 13:02

Wiktor Stribiżew

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7 Comments

Tuan van Duong Over a year ago

How to improve this approach to avoid adding space with number like 1.200 1,200?

Wiktor Stribiżew Over a year ago

@TuanvanDuong /\s*(?<!\d(?=[,.]\d))([,.!?:;]+)(?!\s*$)\s*/g

Tuan van Duong Over a year ago

@ Wiktor Stribiżew I got error SyntaxError: Invalid regular expression: invalid group specifier name with this regex: text = text.replace(/\s*(?<!\d(?=[,.]\d))([,.!?:;]+)(?!\s*$)\s*/g, '$1 ');

Wiktor Stribiżew Over a year ago

@TuanvanDuong You are using an outdated JS engine. So, you can only use text.replace(/\s*(?:\d[,.]\d|([,.!?:;]+))(?!\s*$)\s*/g, function(m, x) { return x ? x+' ' : m;})

Tuan van Duong Over a year ago

@ Wiktor Stribiżew Great, it works now. Thank you so much. Just found 2 minor issues is that if the ... at the end, then it adds space after the second .. And if the . inside a quote, then it still adds space after .. For ex, if the text is I said "Today is a beatiful day.". But tomorrow will be a long day... becomes I said "Today is a beatiful day. ". But tomorrow will be a long day.. .. Any idea?

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Tuan van Duong · Accepted Answer · 2022-09-15 04:19:17Z

Thanks @Wiktor Stribiżew for his suggestions and I come up with the final regex that meets my requirements:

let text = 'Test punctuation:c,c2,c3,d1.D2.D3.Q?.Ec!Sc;Test number:1.200 1,200 2.3.Test:money: $15,000.Test double quote and three dots:I said "Today is a...beautiful,sunny day.".But tomorrow will be a long day...';
text = text.replace(/\.{3,}$|\s*(?:\d[,.]\d|([,.!?:;]+))(?!\s*$)(?!")\s*/g, (m0, m1) => { return m1 ? m1 + ' ' : m0;  });
console.log(text); // It will print out: "Test punctuation: c, c2, c3, d1. D2. D3. Q?. Ec! Sc; Test number: 1.200 1,200 2.3. Test: money: $15,000. Test double quote and three dots: I said "Today is a... beautiful, sunny day.". But tomorrow will be a long day..."

Bonus! I also converted this into Dart as I'm using this feature in Flutter app as well. So just in case someone needs to use it in Dart:

void main() {
  String addSpaceAfterPunctuation(String words) {
    var regExp = r'\.{3,}$|\s*(?:\d[,.]\d|([,.!?:;]+))(?!\s*$)(?!")\s*';
    
    return words.replaceAllMapped(
      RegExp(regExp),
      (Match m) {
        return m[1] != null ? "${m[1]} " : "${m[0]}";
      },
    );
  }
  var text = 'Test punctuation:c,c2,c3,d1.D2.D3.Q?.Ec!Sc;Test number:1.200 1,200 2.3.Test:money: \$15,000.Test double quote and three dots:I said "Today is a...beautiful,sunny day.".But tomorrow will be a long day...';
  text = addSpaceAfterPunctuation(text);
  print(text); // Print out: Test punctuation: c, c2, c3, d1. D2. D3. Q?. Ec! Sc; Test number: 1.200 1,200 2.3. Test: money: $15,000. Test double quote and three dots: I said "Today is a... beautiful, sunny day.". But tomorrow will be a long day...
}

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