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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.

Preserving Newlines When Using ".text" or ".textContent". Possible? Alternatives? Workarounds?

If I grab some html from one element, then attempt to assign it as the text content of another element, newlines are not preserved (at least not in the latest Firefox and Chromium).
So, for example, the follow code (with sensible html) produces output where the newlines are replaced by spaces. Well, except the alert, which works as expected.
$("#info").data("html", $("#info").html());
$("#jquery").text($("#info").data("html"));
document.getElementById("javascript").textContent = $("#info").data("html");
$("#alert").click(function() { alert($("#info").data("html")) });
Here's a running example: http://jsfiddle.net/76S7z/2/
There should be some method of setting the html of one element as the text of another while preserving newlines properly.
Is this possible with "text" or "textContent"? Is there an alternative way to do this? Is there a simple workaround? A less than simple workaround?

As you've already determined, Web browsers don't normally render newline characters \n as line breaks. If you're resistent to adding the line break element <br />, you can use the white-space CSS property with the value pre-line, which will:
Sequences of whitespace are collapsed. Lines are broken at newline characters, at <br>, and as necessary to fill line boxes.
Be sure to check the property's compatibility tables before using.
<div style="white-space: pre-line;">
Look
at
these line breaks!
</div>
Here's a JSFiddle example.

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.

"<" sign not showing in javascript?

I have a div-element that I want to show the symbol '<'.
div-element.innerHMTL = '<';
The string actually do not appears, I think the problem lies in that the browser thinks that it is a beginning of a tag element
Anyone seen this problem before?

You should use an HTML entity - <. This will be displayed by the browser as <, rather than being interpreted as the start of an HTML tag.
Here's a handy list of common HTML entities: http://www.danshort.com/HTMLentities/

divElement.innerHTML = '<';

innerHTML sets does not encode and can be used to set html elements.
innerText sets encodes and cannot be used to set html elements.
You should use innerText when you just want to set text or you should encode the text when you want to mix html with text

This might be useful link which shows all symbols
http://www.w3schools.com/HTML/html_entities.asp