Develop Reference

Angular 9 template interpolation removing backslashes

I need to render a string on the page with double backslash "\\" but Angular removes one from the temaplte, treating it like a regular expression.
An example of the issue is here:
https://codepen.io/bental/pen/xxZdYZv
I have also tried escaping with and without DomSanitizer but can't seem to make it work.
I don't want to manipulate the data as it's coming from the backend and can't account for every possibility

If you don't need IE/Opera support, you can use String.raw (note that you need to use backticks instead of double quotes for it to work as intended)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/raw
this.sanitizer.bypassSecurityTrustHtml(String.raw`Double backslashes are being removed -> \\`);

put \\\\ every \\ represents one \
this.sanitizer.bypassSecurityTrustHtml("Double backslashes are being removed -> \\\\")

When is the HTML attribute backslash escaped as a JavaScript string?

I noticed that backslash is escaped when I get "attribute value including backslash" with JavaScript in the following code.
console.log(document.getElementById("test").getAttribute("class")); // -> \A
console.log(document.getElementById("test").getAttribute("class").replace("\\A", "\A")); // -> A
console.log(document.getElementById("test").dataset.b); // -> \B
console.log(document.getElementById("test").dataset.b.replace("\\B", "\B")); // -> B
<div id="test" class="\A" data-b="\B"></div>
The backslash is treated as a special character in JavaScript, and two backslashes (\\) represent one backslash (\).
The result of the above code means that when getting the attribute value with JavaScript using getAttribute(), one backslash (\) is escaped to two backslashes (\\) at somewhere.
However, in the specification, it seems that the corresponding process is not applied.
Question
In which process of getAttributes() the backslash of HTML attribute is escaped (\ -> \\)?

There's a difference between string literals (which require escaping) and string values from other places (like html, ajax, etc), which are what they look like. Only when converted to literals (ex: JSON.stringify, some console views, etc) do JS strings have backslash escaping. The escape is an output formatting artifact; internally, there are no escapes in the sequence of characters.
HTML doesn't need the same escaping on blackslashes, due to different roots of the standard. An attribute isn't "converted" to one with escaped backslashes unless it's formatted as a string literal. That would happen at a stage between the string and it's visible output. You can use alert() instead of console.log() to see the string as it really is. I believe that specifically for the console, the
goal is to be more helpful to developers than accurate to the internals.

Write HTML Special Character into a Variable

$("<h2/>", {"class" : "wi wi"+data.today.code}).text(" " + data.city + data.today.temp.now + "F").appendTo(custom_example);
Hi there, I'm trying to alter the code above to add the degrees icon just before the (F)arenheit marker. I've tried entering + html("°") + but it doesn't work. My JS is pretty rough and I was hoping I could get a quick answer here before I spent too long trying and failing. Thanks!
I want the end result to print something like: Encinitas 65°F

Special characters are characters that must be escaped by a backslash\, like:
Single quote \'
Double quote \"
Backslash \\
The degree ° is not a special character, you can just write it, as it is.
Edit: If you want to use the unicode of °F, just write: '\u2109'.

Escape Special Characters JavaScript
JavaScript uses the \ (backslash) as an escape characters for:
\' single quote
\" double quote
\ backslash
\n new line
\r carriage return
\t tab
\b backspace
\f form feed
\v vertical tab (IE < 9 treats '\v' as 'v' instead of a vertical tab
('\x0B').
If cross-browser compatibility is a concern, use \x0B instead of \v.)
\0 null character (U+0000 NULL) (only if the next character is not a
decimal digit; else it’s an octal escape sequence)
Note that the \v and \0 escapes are not allowed in JSON strings.

First of all the degree character needs not to be escaped. So simply entering "°F" should do the job.
However, if you are in doubt with the codepage of your JS code you could use a JavaScript escape sequence. JS escape sequences are quite different from HTML escapes. The do not support decimal values at all. So first of all you have to convert 176 to hex: b0. The correctly escaped equivalent to "°F" is "\xb0F". It will work too and is more robust with respect to codepage issues of you platform's source editor.
If you really want to assign HTML code you need to use the .html() function. But this is mutual exclusive to .text(). So in this case all of your content needs to be HTML rather than plain text. Otherwise an HTML injection vulnerability arises. I.e. you need to properly escape angle brackets and some other symbols in data.city and maybe data.today.temp.now as well.
JS itself has no built-in function to escape HTML. But JQuery provides a trick: $('<div/>').text(data.city).html() will return appropriately escaped HTML. See HTML-encoding lost when attribute read from input field for more details.
I would recommend not to use .html() unless you really need it, e.g. if you want to apply styles or formatting to parts of the text only.

Javascript regex ends with pattern

I'm trying to write a regex in javascript to identify string representations of arbitrary javascript functions found in json, ie. something like
{
"key": "function() { return 'I am a function'; }"
}
It's easy enough to identify the start, but I can't figure out how to identify the ending double quotes since the function might also contain escaped double quotes. My best try so far is
/"\s*function\(.*\)[^"]*/g
which works nicely if there are no double quotes in the function string. The end of a json key value will end with a double quote and a subsequent comma or closing bracket. Is there some way to retrieve all characters (including newline?) until a negated pattern such as
not "/s*, and not "/s*}
... or do I need to take a completely different approach without regex?
Here's is the current test data I'm working with:
http://regexr.com/39pvi

Seems like you want something like this,
"\s*function\(.*\)(?:\\.|[^\\"])*
It matches also the inbetween \" escaped double quotes.
DEMO

How can I accommodate a string with both single and double quotes inside of it in JavaScript

I have an application, and it is fed some HTML. It then needs to put that HTML into a string. This HTML contains single and double quotes. Is it possible, in javascript, to declare a string with information inside of it, that does not use single or double quotes?
I guess if it is not possible, does anyone know a simple and easy way to escape these quotes so I can put it in a string? Keep in mind, part of this string will be JavaScript that I will later need to execute.

You need to escape the quotation characters with \:
var someString = 'escape all the quotation marks \"\'';

Is it possible, in javascript, to declare a string with information inside of it, that does not use single or double quotes?
No. JavaScript string literals are delimited with either single quotes or double quotes. Those are the only choices.
does anyone know a simple and easy way to escape these quotes so I can put it in a string?
Do you mean in a string literal?
var str = "var foo=\"bar\"; function say(it) { alert('It is: ' + it); say(foo);";
Or programmatically?
str = str.replace(/"/g, '\\"');

An easy way to escape the quotes is to use the javascript escape function.
http://www.w3schools.com/jsref/jsref_escape.asp

Use the escape function to replace special characters (including single and double quotes). You can then use the unescape function to return the string to it's normal state later if necessary.
For example:
var data = 'hello my name is "James"';
alert(escape(data)); //Outputs: hello%20my%20name%20is%20%22James%22