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How to append newline to text value in javascript array?

I have a narrow button that contains an image and label text. The state of the button changes to one of several values which are stored as text in an array and then changed out with textContent.
One of the values forces a line break in the label text. I would like to reserve the "blank line" below my label so that layout isn't affected every time the label breaks to two lines of text. To accomplish this, I'm trying to append a newline to every single-line value. For layout reasons, I can't simply pad the container — I need it to match the height of a line of formatted text.
Is there any way to put a newline into a text array value? I've tried adding a CR to my text both within the array and prior to the array as a variable using:
Labelname + \n
Labelname\n
Labelname<br /> (HTML, I know)
var label = 'Labelname' + String.fromCharCode(13)
Nothing seems to make the newline "stick," and the console reveals the value "Labelname" without the newline.

HTML generally ignores whitespace (including newline characters). To have it rendered, you need to use an element that doesn't ignore whitespace (like <pre>), or opt in to <pre>-style whitespace handling via CSS with white-space: pre-wrap.

I ended up using innerHTML to put formatted text into the element. I was resistant to using it for various reasons, but it provided a straightforward solution to this problem.

My ID's have been changed, how can i stop it?

I've been trying to do something simple, i think, let me explain:
I have an BPMS software where a send an e-mail at the end of the process, this e-mail is an HTML page that i created, inside the HTML page we have some identifying codes that get a field value from an previously form, some strings. The problem is, when i transfer that value to the HTML page, obviously the "Enter" key doesn't work like the "br" tag, so i made a simple javascript to replace the "enter" for the "br". It worked, but when i send the e-mail my ID is changed and they put an "x_" prefix, so there goes my question.
Can i stop it or there is some other way to do it?
The code is below:
<p id="informacoes">
TEST
TEST
</p>
<script>
var strMessege = document.getElementById('informacoes');
strMessege.innerHTML = strMessege.innerHTML.replace(/(?:\r\n|\r|\n)/g, '<br />');
</script>

It seems like your end goal here is to retain original line breaks present in the source code. I think your best bet would be to address this using CSS.
Take a look at the CSS property white-space, MDN: white-space property
By default, CSS collapses white space (e.g. multiple non-breaking ("regular") spaces, tabs, and newlines) into, effectively, a single regular space. In your example, the line breaks that you see in the source code are being collapsed and so they will not be rendered by the browser or email client.
Try using CSS to set a different white-space property, like
#informacoes {
white-space: pre-line;
/* depending on your use case,
a different value might work better */
}
Property values other than white-space: normal (which is the default) will change whether and how white space, including new lines, are collapsed when rendering from the source code to the screen.

String with new line and tabs to display in HTML

I have a string coming from my java backend which is formatted to display in a certain way, the new line, tab and space characters are in certain positions.
How do I get this to display the same way in HTML?
For example, say I have the current string in Javascript as so:
var str = "\t\tTitle \n Some text \t\t\t more text";

Browsers typically strip out extra white space, you might need to put it inside a preformatted text block or use white-space: pre
var pre = document.createElement("pre");
pre.innerHTML = str;
document.appendChild(pre);
Also yes, you need to use backslahes too, as mentioned about.

I might be late but just in order to help if a beginner like me is facing this kind of problem.
You can add a css class to the html tag where you want to display the data. In my case I am using ngFor of Angular 2. The data coming from my back end had line breaks and tabs. So I just added a class to the html tag with a css white-spacing style as follows.
Backend Data"title": "postIssueResponse() {\n\tthis.parent.postIssueResponse(this.issueId, this.newResponse);\n console.log(this.newResponse);\n this.newResponse \u003d \"\";\n}"
<p class="response-title">{{myData?.title}}</p>
And the css
.response-title {
white-space:pre;
}
This one do the job perfectly.

You can use textarea also. here is a Working Fiddle
MDN textarea

Preserving white space in an HTML select option

I have a set of html text boxes that take input and when the user clicks an 'add' button uses javascript to take the text input and format a string that is put in an HTML select box. The first of these boxes is supposed to contain a 2 character number but can also accept a blank. The formatted strings would look like this:
01-ABC-O
02-DEF-I
However I need a way to display the blank numbers that lines up with the other elements
-GHI-O
This type of entry will show up fine when the javascript adds the option, but when the page is reloaded and the select is repopulated with the values (I'm using Java, jsp, and struts 1.1 if that helps) it gets the same values(spaces preserved) but the whitespace is no longer shown in the select control (I've looked at the page source, and it looks identical to when the javascript adds the option). I have tried substituting the spaces for but this just prints the string "&nbsp" instead of the space. I've also tried using "pre" html blocks and the css white-space property and neither have worked.
Let me know if any further clarification is needed.

You need to replace the spaces with and it should work - note the closing semi-colon (which is missing from your example in the question)! When you do it through Javascript, most (all?) browsers will automatically render the spaces, but when the spaces are there when the page is loaded all (sometimes all but one) of them will be ignored.
You should also apply a font-family: CSS attribute to the select that specifies mono-spaced font(s) in order to ensure everything lines up properly.

When creating the select option with javascript, to preserve white-space, use "\xa0" - it is a NO-BREAK SPACE char.

You can use the pre css style on the area that you are outputting the value to.
<style type="text/css">
#element {
white-space: pre;
}
</style>
<div id="element">
stuff goes here
</div>
This will preserve all whitespace in the div element (other element types will also work) and then you don't need to worry about using the non breaking space.

Are you going to add it via scripting, you need to use Escape Codes for Space "% A0" which you then decode with unescape ()
logTypeList[i] = new Option(unescape(" kent Agent".replace(/ /g, "%A0")), "theValue");

logTypeList[i] = new Option(unescape(" kent Agent".replace(/ /g, "%A0")), "theValue");
Since unescape is deprecated, you may want to use decodeURI:
logTypeList[i] = new Option(decodeURI(" kent Agent".replace(/ /g, "%C2%A0")), "theValue");
More info at http://www.javascripter.net/faq/mathsymbols.htm

You can use the Unicode Character 'SPACE' (U+0020) instead of ("\u0020")

Quote in HTML attribute destroys layout

My site has user generated content. I noticed that if the user has quotes in some text and later I displayed that text in an HTML attribute, the layout would get screwed up in IE.
Hello
However, if I had generated the same anchor with Javascript (Prototype library), the layout would not be screwed up in IE:
$$('body').first().appendChild(
new Element(
'a', {
title: 'user "description" of link',
href: 'link.html'
}
).update('Hello')
);
Why is this so? The JS and the plain HTML versions both have the same intended result, but only the JS doesn't screw up IE. What's happening behind the scenes?
BTW, I do strip_tags() and clean XSS attacks from all user input, but I don't strip all HTML entities because I use a lot of form text input boxes to display back user generated text. Form elements literally display HTML entities, which looks ugly.

You need to escape all output that is user-specified (using entities). The DOM-methods do that automatically.

I don't know how you are processing the user generated content, but you could use a replace function to clean up the input something like string.replace("\"", "")

The answer to your question: 'Why is it so' is because in your JavaScript example set the title attribute with single quotes. So the double quotes in the user generated string are already escaped.
In you A tag example, single quotes around the text you use in the title attribute may be a way to solve the rendering problem.
However, Your HTML attributes should be in double quotes, so you would be better off using entities, as suggested by #elusive in his answer.