JavaScript: how to use a regular expression to remove blank lines from a string?

Question

I need to use JavaScript to remove blank lines in a HTML text box. The blank lines can be at anywhere in the textarea element. A blank line can be just a return or white spaces plus return.

I am expecting a regular expression solution to this. Here are some I tried, but they are not working and cannot figure out why:

/^\s*\r?\n/g   

/^\s*\r?\n$/g

Edit 1

It appears that the solution (I modified it a little) suggested by aaronman and m.buettner works:

string.replace(/^\s*\n/gm, "") 

Can someone tell why my first regular expression is not working?

Edit 2

After reading all useful answers, I came up with this:

/^[\s\t]*(\r\n|\n|\r)/gm

Is this going to be one that cover all situations?

Edit 3

This is the most concise one covering all spaces (white spaces, tabs) and platforms (Linux, Windows, Mac).

/^\s*[\r\n]/gm

Many thanks to m.buettner!

Janinajanine

I am expecting a regular expression solution to this. Eat healthy and post the RegExp here if it doesn't work – Returnee

Tag in title: check, No code: check, Wrong attitude: check, Ironic thanks message: check, Downvote: check. – Donall

Even if you're new to this site you can search it for something like regex blank lines or something. You can see from example what will be answered and what will be voted right off the map... for example: #3013288 - that answers your needs – Daytoday

Hello folks, I did try a number regular expressions myself, but simply cannot get it done. And I googled for it. Try my title in google search and show me where you get the answer. – Janinajanine

right, so update your question with code you tried. we will show you what you did wrong. The way it is it looks like you want us to do your work for you – Daytoday

I would do it like this: 'Line1\n\nLine3'.split(/\r?\n/).filter(Boolean).join('\n') – Hydromechanics

Answer 1

Your pattern seems alright, you just need to include the multiline modifier m, so that ^ and $ match line beginnings and endings as well:

/^\s*\n/gm

Without the m, the anchors only match string-beginnings and endings.

Note that you miss out on UNIX-style line endings (only \r). This would help in that case:

/^\s*[\r\n]/gm

Also note that (in both cases) you don't need to match the optional \r in front of the \n explicitly, because that is taken care of by \s*.

As Dex pointed out in a comment, this will fail to clear the last line if it consists only of spaces (and there is no newline after it). A way to fix that would be to make the actual newline optional but include an end-of-line anchor before it. In this case you do have to match the line ending properly though:

/^\s*$(?:\r\n?|\n)/gm

Higgledypiggledy

m.buettner, thanks so much for pointing out the Mac scenario. – Janinajanine

m.buettner, I created a new one /^[\s\t]*(\r\n|\n|\r)/gm. Is it going to cover all situations? – Janinajanine

@curious1, \s includes all white space. That is spaces, \t, \r and \n. That was the point of using \s in the first place. Therefore, our patterns do exactly the same, and yes, they both cover all cases. – Higgledypiggledy

m.buettner, thanks so much for the detailed and crystal-clear explanation. best. – Janinajanine

This will fail if the last line is blank because there is no carriage return, probably the most common case. Needs a question mark. /^\s*[\r\n]?/gm – Amaral

@Amaral that doesn't work. It would remove leading whitespace from all lines. You'd have to insert a $ in front of the character class. It's a good catch though, I'll edit the answer. – Higgledypiggledy

Strings with \r\n as newline will not work: "a\r\nb".replace(/^\s*$(?:\r\n?|\n)/gm, '')==="ab" – Fortune

Answer 2

I believe this will work

searchText.replace(/(^[ \t]*\n)/gm, "")

Merlon

This will not allow for \r\n or any other whitespace in front of the line break. – Higgledypiggledy

fixed it, his original post did not say that a line was empty if it had actual spaces in it – Merlon

aaronman, thanks for the additional code to catch \t. appreciate it! – Janinajanine

Answer 3

This should do the trick i think:

var el = document.getElementsByName("nameOfTextBox")[0];
el.value.replace(/(\r\n|\n|\r)/gm, "");

EDIT: Removes three types of line breaks.

Amati

He mainly wants to remove new-line characters – Returnee

ahh.. time to get to sleep i think ;) – Apodal

This will remove all line breaks (not just empty lines), and the m is redundant. – Higgledypiggledy

Bjørn Bråthen, thanks for showing all three types of line breaks, which is really new to me. Thanks, again! – Janinajanine

\r\n is usually windows, \n linux and \r mac if I recall correctly. – Apodal

Answer 4

Here's a reusable function that will trim each line's whitespace and remove any blank or space-only lines:

function trim_and_remove_blank_lines(string)
{
    return string.replace(/^(?=\n)$|^\s*|\s*$|\n\n+/gm, "")
}

Usage example:

trim_and_remove_blank_lines("Line 1 \nLine2\r\n\r\nLine4\n")

//Returns 'Line 1\nLine2\nLine4'

Envision

Answer 5

function removeEmptyLine(text) {
  return text.replace(/(\r?\n)\s*\1+/g, '$1');
}

test:

console.assert(removeEmptyLine('a\r\nb') === 'a\r\nb');
console.assert(removeEmptyLine('a\r\n\r\nb') === 'a\r\nb');
console.assert(removeEmptyLine('a\r\n \r\nb') === 'a\r\nb');
console.assert(removeEmptyLine('a\r\n \r\n  \r\nb') === 'a\r\nb');
console.assert(removeEmptyLine('a\r\n \r\n 2\r\n  \r\nb') === 'a\r\n 2\r\nb');
console.assert(removeEmptyLine('a\nb') === 'a\nb');
console.assert(removeEmptyLine('a\n\nb') === 'a\nb');
console.assert(removeEmptyLine('a\n \nb') === 'a\nb');
console.assert(removeEmptyLine('a\n \n  \nb') === 'a\nb');
console.assert(removeEmptyLine('a\n \n2 \n  \nb') === 'a\n2 \nb');

Fortune