Trim trailing spaces before newlines in a single multi-line string in JavaScript

Question

Say I have this single string, here I denote spaces (" ") with ^

^^quick^^^\n
^brown^^^\n
^^fox^^^^^\n

What regular expression to use to remove trailing spaces with .replace()? using replace(/\s+$/g, "") not really helpful since that only removes the spaces on the last line with "fox".

Going through other questions I found that replace(/\s+(?:$|\n)/g,"") matches the right sections but also gets rid of the new line characters but I do need them.

So the perfect result will be:

^^quick\n
^brown\n
^^fox\n

(only trailing spaces are removed; everything else stays)

ridgerunner · Accepted Answer · 2013-11-17 23:43:43Z

24

Add the 'm' multi-line modifier.

replace(/\s+$/gm, "")

Or faster still...

replace(/\s\s*$/gm, "")

Why is this faster? See: Faster JavaScript Trim

Addendum: The above expression has the potentially unwanted effect of compressing adjacent newlines. If this is not the desired behavior then the following pattern is preferred:

replace(/[^\S\r\n]+$/gm, "")

Edited 2013-11-17: - Added alternative pattern which does not compress consecutive newlines. (Thanks to dalgard for pointing this deficiency out.)

edited Nov 17, 2013 at 23:43

answered Apr 6, 2011 at 15:21

ridgerunner

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2 Comments

leonard vertighel Over a year ago

What about if I would like to include leading spaces in replace(/[^\S\r\n]+$/gm, "") ?

ridgerunner Over a year ago

@leonard vertighel - This one should do the trick: replace(/^[^\S\r\n]+|[^\S\r\n]+$/gm, "")

tanguy_k · Accepted Answer · 2024-11-18 21:34:35Z

0

Use String.prototype.trimEnd() (or trim()):

multilineText.split('\n').map(line => line.trimEnd()).join('\n');

Regex are hard to read and understand, favor simple functions composition when possible.

const multilineText = '  quick   \n brown   \n  fox     \n';

const multilineTextTrimmed = multilineText
  .split('\n')
  .map(line => line.trimEnd())
  .join('\n');

console.log(multilineTextTrimmed);

console.assert(multilineTextTrimmed === '  quick\n brown\n  fox\n');

edited Nov 18, 2024 at 21:34

answered Nov 8, 2024 at 19:23

tanguy_k

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