Little tool to identify and convert line terminators from strings.

Install

npm i line-terminators

Usage

Identify line terminators from a string

import lt from 'line-terminators'

lt.identify('abc\ndef') // => "LF"

lt.identify('abc\r\ndef') // => "CRLF"

lt.identify('abcdef') // => "NONE"

Convert a string's line terminators to another format

import lt from 'line-terminators'

lt.convert('abc\ndef', 'CRLF') // => "abc\r\ndef"

lt.convert('abc\r\ndef', 'LF') // => "abc\ndef"

// It will keep the original line terminators if the target is NONE
lt.convert('abc\r\ndef\r\nghi', 'NONE') // => "abc\r\ndef\r\nghi"

// If you want it to delete the line terminators when the target is NONE,
// then pass the third parameter as `true`

lt.convert('abc\r\ndef\r\nghi', 'NONE', true) // => "abcdefghi"

Note: Passing null or undefined works the same as 'NONE'

Copy the line terminators from a string into another

import lt from 'line-terminators'

lt.copy('abc\r\ndef\r\nghi', 'tuv\nxyz') // => "tuv\r\nxyz"

lt.copy('abc\ndef\nghi', 'tuv\r\nxyz') // => "tuv\nxyz"

// Keeps line terminators when the source string has no line terminators

lt.copy('abcdefghi', 'tuv\nxyz') // => "tuv\nxyz"

lt.copy('abcdefghi', 'tuv\r\nxyz') // => "tuv\r\nxyz"

// If you want it to delete the line terminators when the source string has no
// line terminators, then pass the third parameter as `true`

lt.copy("abcdefghi", "tuv\nxyz", true) // => "tuvxyz"
lt.copy("abcdefghi", "tuv\r\nxyz", true) // => "tuvxyz"

Real-life use case

Imagine you want to read a JSON file, manipulate it and save it. You would probably write something as simple as:

const content = JSON.parse(fs.readFileSync(filePath))

content.myProperty = 'my value'

fs.writeFileSync(filePath, JSON.stringify(content, null, 2))

This should be ok for most cases, but if you are working on a Windows machine and the original file was written in a POSIX machine, then you're also changing the line terminators from LF to CRLF.

Also, imagine that myProperty already had my value in the original file. It will end up producing no changes to your content, but the file will still be different. If you use git, you will see a file change.

You may even try to prevent writing the file if it has no changes, like:

const contentString = fs.readFileSync(filePath)

const contentObject = JSON.parse(contentString)

contentObject.myProperty = 'my value'

const result = JSON.stringify(contentObject, null, 2)

if (result === contentString) {
  return
}

fs.writeFileSync(filePath, result)

But result === contentString would evaluate to false, as the line terminators are different between those strings.

By using this little tool, you could do:

import lt from 'line-terminators'

const contentString = fs.readFileSync(filePath)

const contentObject = JSON.parse(contentString)

contentObject.myProperty = 'my value'

let result = JSON.stringify(contentObject, null, 2)

// Copy the line terminators from contentString to result
result = lt.copy(contentString, result)

if (result === contentString) {
  return
}

fs.writeFileSync(filePath, result)

result === contentString would now evaluate to true, since the result now uses the same line terminators as the contentString string.