What is the JavaScript string newline character?

Is \n the universal newline character sequence in JavaScript for all platforms? If not, how do I determine the character for the current environment?

I'm not asking about the HTML newline element (<BR/>). I'm asking about the newline character sequence used within JavaScript strings.

I've just tested a few browsers using this silly bit of JavaScript:

function log_newline(msg, test_value) {
  if (!test_value) { 
    test_value = document.getElementById('test').value;
  }
  console.log(msg + ': ' + (test_value.match(/\r/) ? 'CR' : '')
              + ' ' + (test_value.match(/\n/) ? 'LF' : ''));
}

log_newline('HTML source');
log_newline('JS string', "foo\nbar");
log_newline('JS template literal', `bar

baz`);

<textarea id="test" name="test">

</textarea>

IE8 and Opera 9 on Windows use \r\n. All the other browsers I tested (Safari 4 and Firefox 3.5 on Windows, and Firefox 3.0 on Linux) use \n. They can all handle \n just fine when setting the value, though IE and Opera will convert that back to \r\n again internally. There's a SitePoint article with some more details called Line endings in Javascript.

Note also that this is independent of the actual line endings in the HTML file itself (both \n and \r\n give the same results).

When submitting a form, all browsers canonicalize newlines to %0D%0A in URL encoding. To see that, load e.g. data:text/html,<form><textarea name="foo">foo%0abar</textarea><input type="submit"></form> and press the submit button. (Some browsers block the load of the submitted page, but you can see the URL-encoded form values in the console.)

I don't think you really need to do much of any determining, though. If you just want to split the text on newlines, you could do something like this:

lines = foo.value.split(/\r\n|\r|\n/g);

Yes, it is universal.

Although '\n' is the universal newline characters, you have to keep in mind that, depending on your input, new line characters might be preceded by carriage return characters ('\r').

Don't use "\n". Just try this:

var string = "this\
is a multi\
line\
string";

Just enter a backslash and keep on trucking! It works like a charm.

It might be easiest to just handle all cases of the new line character instead of checking which case then applying it. For example, if you need to replace the newline then do the following:

htmlstring = stringContainingNewLines.replace(/(\r\n|\n|\r)/gm, "<br>");

Yes, use \n, unless you are generating HTML code, in which case you want to use <br />.

In an email link function, I use "%0D%0A":

function sendMail() {
    var bodydata="Before "+ "%0D%0A";
        bodydata+="After"

    var MailMSG = "mailto:[email protected]"
             + "[email protected]"
             + "&subject=subject"
             + "&body=" + bodydata;
    window.location.href = MailMSG;
}

HTML

<a href="#" onClick="sendMail()">Contact Us</a>

You can use `` quotes (which are below the Esc button) with ES6. So you can write something like this:

var text = `fjskdfjslfjsl
skfjslfkjsldfjslfjs
jfsfkjslfsljs`;

Get a line separator for the current browser:

function getLineSeparator() {
  var textarea = document.createElement("textarea");
  textarea.value = "\n"; 
  return textarea.value;
}

A note - when using ExtendScript JavaScript (the Adobe Scripting language used in applications like Photoshop CS3+), the character to use is "\r". "\n" will be interpreted as a font character, and many fonts will thus have a block character instead.

For example (to select a layer named 'Note' and add line feeds after all periods):

var layerText = app.activeDocument.artLayers.getByName('Note').textItem.contents;
layerText = layerText.replace(/\. /g,".\r");

printAccountSummary: function()
    {return "Welcome!" + "\n" + "Your balance is currently $1000 and your interest rate is 1%."}
};
console.log(savingsAccount.printAccountSummary()); // Method

Prints:

Welcome!
Your balance is currently $1000 and your interest rate is 1%.

I had the problem of expressing newline with \n or \r\n.
Magically the character \r which is used for carriage return worked for me like a newline.
So in some cases, it is useful to consider \r too.

I believe it is -- when you are working with JavaScript strings.

If you are generating HTML, though, you will have to use <br /> tags (not \n, as you're not dealing with JavaScript any more).

A practical observation... In my Node.js script I have the following function:

function writeToLogFile (message) {
    fs.appendFile('myserverlog.txt', Date() + " " + message + "\r\n", function (err) {
        if (err) 
            throw err;
    });
}

First, I had only "\n", but I noticed that when I open the log file in Notepad, it shows all entries on the same line. Notepad++, on the other hand, shows the entries each on their own line. After changing the code to "\r\n", even Notepad shows every entry on its own line.

The \n is just fine for all cases I've encountered. If you are working with web, use \n and don't worry about it (unless you have had any newline-related issues).

You can use <br/> and the document.write/ and document.writeln one.