Remove all line-breaks, but except only one break?

Question

I have the following text sent by the user with breaklines

Text of example in line 1.
(break line)
(break line)
(break line)
The text is very nice...
(break line)
(break line)
The end.

Result expected:

Text of example in line 1.
The text is very nice...
The end.

NOT: Text of example in line 1. The text is very nice... The end.

How I do this in JavaScript(str.replace) receiving via AJAX in PHP

$text = strip_tags($text, '<br>');

Thank you for answers! But I tested all .. and then I went to see that my DIV is generating HTML codes, I believe that is why it is not working (RegEx). How do I ignore HTML elements to be able to text with line breaks?

score 5 · Accepted Answer · answered Feb 26 '16 at 23:44

5

You can use a regex replace.

str = str.replace(/\n{2,}/g, "\n");

{2,} means to match 2 or more of the previous expression. So any sequence of 2 or more newlines will be replaced with a single newline.

answered Feb 26 '16 at 23:44

Barmar

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1

Since you're replacing with the same char, it doesn't hurt to just replace all `str = str.replace(/\n+/g, "\n");` – trex005 Feb 26 '16 at 23:54
1

@trex005 This is slightly more efficient, since it doesn't bother replacing a single newline with itself. – Barmar Feb 26 '16 at 23:55
1

You are correct, drastically more efficient: http://jsperf.com/regex-replace-multi-single – trex005 Feb 27 '16 at 00:02
1

Wow, I'm surprised there's so much difference when there are no single newlines in your sample text. – Barmar Feb 27 '16 at 00:26
1

In HTML, line breaks are `
`. – Barmar Feb 28 '16 at 03:36
1

If you're working with the DOM, you shouldn't use regular expressions. Use DOM methods to remove elements. – Barmar Feb 28 '16 at 03:37
1

You can also use CSS to change how the DIV is displayed. – Barmar Feb 28 '16 at 03:37
i have this sequence: `1

2

3

4

5`. how do I leave only 2 `
`? `1

2

3

4

5` – Fábio Zangirolami Feb 28 '16 at 18:35
str.replace(/(
){2,}/gi, '

'); tks ;) – Fábio Zangirolami Feb 28 '16 at 18:48
You should use `{3,}`, since you don't need to replace anything when there are already only 2 copies. – Barmar Feb 29 '16 at 15:40

score 5 · Answer 2 · edited May 23 '17 at 12:01

Although, the answer by @Barmar is correct, it'll not work across different OS/platforms.

Different OS uses different character combination to use as linebreak.

Windows: \r\n = CR LF
Unix/Linux: \n = LF
Mac: \r = CR

See \r\n , \r , \n what is the difference between them?

I'll suggest the following RegEx that will work across platforms.

str = str.replace(/(\r\n?|\n){2,}/g, '$1');

Live RegEx Demo

Explanation:

(): Capturing group
\r\n?: Matches \r followed by \n optionally. Thus matches
- \r\n OR
- \r
|: OR condition in RegEx
\n: Match \n
{2,}: Match previous character/s two or more times
g: Global flag
$1: The first captured group I.e a single line-break character supported by OS.

Remove all line-breaks, but except only one break?

2 Answers2

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