regex - replace multi line breaks with single in javascript

Question

this is some kind of variable content in javascript:

    <meta charset="utf-8">

    <title>Some Meep meta, awesome</title>




    <-- some comment here -->
    <meta name="someMeta, yay" content="meep">

</head>

I want to reduce the multi line breaks (unknown number) to a single line break while the rest of the formatting is still maintained. This should be done in javascript with a regex.

I have problems with the tabulator or to keep the format.

Why? This won't update or change the source of the page, and I can't believe that white-space is an issue in the DOM (if it's preserved at all). I'm not saying you shouldn't do this, but I can't see why it benefits you. So there might be another approach to the problem, which is a better solution. — David Thomas
– David Thomas, Commented Jun 10, 2012 at 0:11
So it's replacing/removing white-space in text presented on-screen? Not in the actual HTML source/DOM of the page itself? — David Thomas
– David Thomas, Commented Jun 10, 2012 at 0:14
"This should be done in javascript with a regex." --- sounds like a job description — zerkms
– zerkms, Commented Jun 10, 2012 at 0:19

poke · Accepted Answer · 2012-06-10 02:01:20Z

108

Try this:

text.replace(/\n\s*\n/g, '\n');

This basically looks for two line breaks with only whitespace in between. And then it replaces those by a single line break. Due to the global flag g, this is repeated for every possible match.

edit:

is it possibile to leave a double line break instead of a single

Sure, simplest way would be to just look for three line breaks and replace them by two:

text.replace(/\n\s*\n\s*\n/g, '\n\n');

If you want to maintain the whitespace on one of the lines (for whatever reason), you could also do it like this:

text.replace(/(\n\s*?\n)\s*\n/, '$1');

edited Jun 10, 2012 at 2:01

answered Jun 10, 2012 at 0:21

poke

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5 Comments

e382df99a7950919789725ceeec126 Over a year ago

is it possibile to leave a double line break instead of a single, that i have a distance between the lines ? :)

Amer Mograbi Over a year ago

I tried your solution and it works but I don't understand why. I read that regex is matched "eagerly", meaning that it takes the first match it finds. Why doesn't this regex match every two adjacent newlines and replaces it with one newline then?

poke Over a year ago

@AmerMograbi It does take two adjacent newlines and replace it by a single one. For example running this on foo\n\nbar will return foo\nbar. The eager matching usually refers to the fact that regular expressions will match as much as they can get, which is why this expression works to match multiple line breaks, e.g. \n\n\n. Otherwise, it would just match the first line break, then match nothing for the \s* and match the second line break, leaving the third one untouched.

Amer Mograbi Over a year ago

@poke Oh, I get it now, thanks! It seems that I misunderstood what they meant by "eager".

matt Over a year ago

its got to be worth noting sometimes the line break will be represented as \r\n, might save you a few minutes

mVChr · Accepted Answer · 2012-06-10 00:23:11Z

20

myText = myText.replace(/\n{2,}/g, '\n');

See demo

answered Jun 10, 2012 at 0:23

mVChr

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Comments

David Thomas · Accepted Answer · 2012-06-10 00:24:00Z

3

Given the following (remember to encode HTML entities such as <, > and (among others, obviously) &):

<pre>
&lt;head&gt;

    &lt;meta charset="utf-8"&gt;

    &lt;title&gt;Some Meep meta, awesome&lt;/title&gt;




    &lt;-- some comment here -->
    &lt;meta name="someMeta, yay" content="meep"&gt;

&lt;/head&gt;
</pre>
<pre>
</pre>

The following JavaScript works:

var nHTML = document.getElementsByTagName('pre')[0].textContent.replace(/[\r\n]{2,}/g,'\r\n');
document.getElementsByTagName('pre')[1].appendChild(document.createTextNode(nHTML));

JS Fiddle demo.

answered Jun 10, 2012 at 0:24

David Thomas

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Comments

miqrc · Accepted Answer · 2020-09-01 16:22:08Z

1

To replace all the extra line breaks and leave only one use:

myText = myText.replace(/\n\n*/g,'\r\n');

answered Sep 1, 2020 at 16:22

miqrc

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1 Comment

Yasir Over a year ago

Uncaught SyntaxError

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