javascript - Line endings (also known as Newlines) in JS strings - Stack Overflow

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It is well known, that Unix-like system uses LF characters for newlines, whereas Windows uses CR+LF.

However, when I test this code from local HTML file on my Windows PC, it seems that JS treat all newlines as separated with LF. Is it correct assumption?

var string = `
    foo




    bar
`;

// There should be only one blank line between foo and bar.

// \n - Works
// string = string.replace(/^(\s*\n){2,}/gm, '\n');

// \r\n - Doesn't work
string = string.replace(/^(\s*\r\n){2,}/gm, '\r\n');

alert(string);

// That is, it seems that JS treat all newlines as separated with 
// `LF` instead of `CR+LF`?

It is well known, that Unix-like system uses LF characters for newlines, whereas Windows uses CR+LF.

However, when I test this code from local HTML file on my Windows PC, it seems that JS treat all newlines as separated with LF. Is it correct assumption?

var string = `
    foo




    bar
`;

// There should be only one blank line between foo and bar.

// \n - Works
// string = string.replace(/^(\s*\n){2,}/gm, '\n');

// \r\n - Doesn't work
string = string.replace(/^(\s*\r\n){2,}/gm, '\r\n');

alert(string);

// That is, it seems that JS treat all newlines as separated with 
// `LF` instead of `CR+LF`?

• javascript
• regex
• eol

Share Improve this question Follow asked Apr 22, 2018 at 16:19 john c. j.john c. j. 1,19555 gold badges3737 silver badges9292 bronze badges 4

• What's weird? linebreaks are not converted automatically when you open in another OS. – revo Commented Apr 22, 2018 at 16:58
• What editor are you using, a half decent editor won't care. – Keith Commented Apr 22, 2018 at 17:03
• Do you retrieve your code via a Git client? There is a setting to convert ` \r\n` automatically. There are also some editors that do a similar thing. – wp78de Commented Apr 22, 2018 at 23:00
• @wp78de No, I don't use Git (I'm not fulltime developer, it's just a hobby). The question itself is more about research, self-education, rather then solving some real problem. – john c. j. Commented Apr 23, 2018 at 1:31

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 4

I think I found an explanation.

You are using an ES6 Template Literal to construct your multi-line string.

According to the ECMAScript specs a

.. template literal ponent is interpreted as a sequence of Unicode code points. The Template Value (TV) of a literal ponent is described in terms of code unit values (SV, 11.8.4) contributed by the various parts of the template literal ponent. As part of this process, some Unicode code points within the template ponent are interpreted as having a mathematical value (MV, 11.8.3). In determining a TV, escape sequences are replaced by the UTF-16 code unit(s) of the Unicode code point represented by the escape sequence. The Template Raw Value (TRV) is similar to a Template Value with the difference that in TRVs escape sequences are interpreted literally.

And below that, it is defined that:

The TRV of LineTerminatorSequence::<LF> is the code unit 0x000A (LINE FEED).
The TRV of LineTerminatorSequence::<CR> is the code unit 0x000A (LINE FEED).

My interpretation here is, you always just get a line feed - regardless of the OS-specific new-line definitions when you use a template literal.

Finally, in JavaScript's regular expressions a

\n matches a line feed (U+000A).

which describes the observed behavior.

However, if you define a string literal '\r\n' or read text from a file stream, etc that contains OS-specific new-lines you have to deal with it.

Here are some tests that demonstrate the behavior of template literals:

`a
b`.split('')
  .map(function (char) {
    console.log(char.charCodeAt(0));
  });

(String.raw`a
b`).split('')
  .map(function (char) {
    console.log(char.charCodeAt(0));
  });
  
 'a\r\nb'.split('')
  .map(function (char) {
    console.log(char.charCodeAt(0));
  });
  
"a\
b".split('')
  .map(function (char) {
    console.log(char.charCodeAt(0));
  });

Interpreting the results:
char(97) = a, char(98) = b
char(10) = \n, char(13) = \r

You could use the regular expression: /^\s*[\r\n]/gm

Code example:

let string = `
    foo




    bar
`;

string = string.replace(/^\s*[\r\n]/gm, '\r\n');

console.log(string);

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