In NodeJS, how do you print lines to a file without manually adding the new line character?

Question

I'm trying to figure out how to simply write a string representing a line to a file, where whatever function I call automatically appends a newline character.

I've tried using the default NodeJS file system library for this but I can't get this to work in any way without manually appending '\n' to the string.

Here's the code I tried:

const fs = require('fs');
const writer = fs.createWriteStream('test.out.txt', { flags: 'w' })

writer.write('line 1')
writer.write('line 2');
writer.write('line 3');
writer.end('end');

However, the output file test.out.txt contains the following line with no newline characters:

line 1line 2line 3end

I would like it to look like this:

line 1
line 2
line 3
end

Note that I'm not trying to log messages, and I'm not trying to redirect standard output.

Is there any way to print it this way with the new line characters automatically added?

I was hoping that there's a built-in way to do this. C has `sprintf()`, Java has `println()`. Surely there's a way in Javascript to do this. — Charles Spencer, Mar 12 '18 at 19:16
possible duplicate of (https://stackoverflow.com/questions/3459476/how-to-append-to-a-file-in-node) — Ryan Wilson, Mar 12 '18 at 19:16
It's not a duplicate of that one since that one is talking about appending strings to a file. I actually don't want to append data, although it doesn't really matter to me for this question. — Charles Spencer, Mar 12 '18 at 19:17
Are you worried about cross platform EoL issues? See [node EoL](https://nodejs.org/api/os.html#os_os_eol) — zero298, Mar 12 '18 at 19:20
@zero298 Not necessarily. I was just hoping for a convenient, built-in way to do this, or maybe an NPM library? — Charles Spencer, Mar 12 '18 at 19:23

Matt Mokary · Answer 1 · 2018-03-12T19:25:24.673

1

Manually appending the \n isn't so bad.

You could write a wrapper function to avoid having to put the + '\n' everywhere:

const os = require('os');

let writeln = function (writeStream, str) {
    writeStream.write(str + os.EOL);
}

writeln(writer, 'line 1');
writeln(writer, 'line 2');
writeln(writer, 'line 3');
writeln(writer, 'end');

From what I can tell by a cursory look over the fs.WriteStream docs, there's no native writeln function, or anything similar.

edited Mar 12 '18 at 19:25

answered Mar 12 '18 at 19:19

Matt Mokary

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but it is better to use `os.EOL` instead of hard-coded '\n' – RidgeA Mar 12 '18 at 19:20
So I should also add that my goal is to use NodeJS to make several command line programs, so if I add code myself to do this, I'd have to make a library they could all share. Is there already a library out there? – Charles Spencer Mar 12 '18 at 19:21
1

Thanks @RidgeA, edited. There could very well be a library out there that would add these couple lines for you, but it could also do things you don't want and you may have to fight with it to narrow it down to your specific purpose. This is a case in which it probably makes sense to create a shared utility that you maintain, and that does exactly what you need it to. – Matt Mokary Mar 12 '18 at 19:25

Christian Benseler · Accepted Answer · 2018-03-12T19:27:10.580

1

As mentioned in the comments, you can write a function to add a text as a line

const writeLine = (writerObject, text) => {
  writerObject.write(`${text}\n`)
}
writeLine(writer, 'line 1')
writeLine(writer, 'line 2')
writeLine(writer, 'line 3')

Or you can also use a clojure to create a wrapper object that keeps the 'writer' instead of passing it every time

const customWriter = writerObject => {
  return text => writerObject.write(`${text}\n`)
}

const yourWriterWithBreakLine = customWriter(writer)
yourWriterWithBreakLine('line 1')
yourWriterWithBreakLine('line 2')
yourWriterWithBreakLine('line 3')

edited Mar 12 '18 at 19:27

answered Mar 12 '18 at 19:20

Christian Benseler

7,907
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If you're going to use a closure, you could pass 2 arguments: the writer and the EOL character ('\n' or '\r\n' or os.EOL if you're using the "os" module). – Sébastien Mar 12 '18 at 19:29
Accepting this answer because I like the closure idea. – Charles Spencer Mar 12 '18 at 19:46

In NodeJS, how do you print lines to a file without manually adding the new line character?

2 Answers2