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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.

Formatting text from process to HTML

I am output from a process in python to be displayed on a webpage, however I am unable to format this text properly as <br>, \n and \t is rendered onto the page.
Attempts
Replace \n with <br> or <\br>, then place changed text into <p> tag
Use a <pre> tag with the unformatted text containing \n and \t
encode the text as unicode on the server line = unicode(output.strip())
removing all quotes from within string
Tried using python html module but characters rendered as is line = html.escape(output.strip())
Note
I am using React so I cannot edit the DOM directly, I have to manipulate state.
Example lines
unformated i.e. leaving newlines etc
<pre className='console_text' key={i}>{el}</pre>
or (with replacements) i.e. replace newlines with br tag and tabs with spacing character
<p className='console_text' key={i}>{el}</p>
Note also
I am able to send other text from the server myself which contains newlines and it is formatted properly, I believe it has something to do with either the text formatting or some hidden character(s) that escapes everything but I am unable to find it, I'd appreciate any guidance.
Console output

You need to escape HTML characters, see Escaping HTML

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")

Displaying <textarea> value as HTML

I have a form with several textarea elements. User enters data and submits the form. On the next page it shows submitted text as static text - in p tags. Obviously New Line and multiple paces get ignored and everything just shows in one line.
I can do some preprocessing like replacing New line characters with "br/" and spaces with . but I was wondering if there is a standard solution to that either on server side (C#) or client side (javascript)

Since the data is preformatted (and this isn't just a matter of presentation), the pre element would be suitable (you will still need to replace <, & and friends with the appropriate entities).

Apply CSS white-space: pre; on the <p> element. This way any whitespace inside the element will be preserved.

Actually, I ended up replacing new line symbol with [br/] and it works very well.

How do you make linebreaks in a HTML textarea result in breaks in the string?

I have a HTML <textarea> that I want to be able to make when the user pushes enter in the textarea it results in a linebreak when the string is stored in a variable and printed on the page.
How would I do this? I have seen it done before but I am not sure how to do it.

When you read the content of textarea just do this:
var text = document.getElementById(textAreaId).value.replace("\n","<br/>");
By this way, when you use the variable text, it will be able to break lines in html.

You should set the white-space property on your output to one of the pre values. See here for a list of allowed values and their effects: http://www.w3schools.com/CSS/pr_text_white-space.asp
<p style="white-space: pre;">Your text with newlines goes here.</p>
Or simply use <pre>, a HTML tag that has white-space: pre; by default, but this has the inconvenient of changing your font.
I would advise against storing <br />s instead of new line characters. If you want to have HTML breaks add them just to the output.

Assuming you are outputting as HTML, you'll need to replace the line breaks with <br> or wrap the text with the <pre> tag.
The <pre> tag defines preformatted
text.
Text in a pre element is displayed in
a fixed-width font (usually Courier),
and it preserves both spaces and line
breaks.